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FRONTISPIECE

EIGENMANN

Entrance of Ariguanabo River, Cuba, to its underground channel at San Antonio de los Bajos.

CAVE VERTEBRATES OF AMERICA

A STUDY IN DEGENERATIVE EVOLUTION

BY

CARL H. EIGENMANN

PROFESSOR OF ZOOLOGY, INDIANA UNIVERSITY

WASHINGTON, D.C.

PUBLISHED BY THE CARNEGIE INSTITUTION OF WASHINGTON

JUNE, 1909

Olid

CARNEGIE INSTITUTION OF WASHINGTON

PuBLicaTION No, 104

STEJNEGER * COLLECTION

QLetiona yuses

Norwood Yress . J. 8. Cushing Co, Berwick & Smith Co. Norwood, Mass., U.S.A. : -

CONTENTS.

PAGE

preface: : : c 6 : : : : é : . 5 0 c 3 ; - vil

Introductory. : 3 : 3 : : 5 5 5 : : 9 : 5 . Vii

Acknowledgments. : ¢ : 5 : a : é : é ; é 5 . vill

Conclusions of General Import . : : : é , : ; : ; ax

A General Consideration of Caves and the Cae pana I

Caves and the Cave Fauna 3

Caves in their Relation to the Rest of the Unierce 3

The Nature of the Cave Environment : : é ° : 4 : 5

The Blind Vertebrates and Cave Vertebrates of North Ame : 9

The Origin and Dispersal of Cave Animals . c : : : 3 : : . é 5 OL

The Origin of the Food Supply of Caves. : : : : : : 5 uy

Age of Caves in their Relation to the Variety of Gaye pane 5 : : F : : 5 ty

Divergence in Epigean and Convergence in Subterranean Fishes . . : . : 2 a8 Conclusions : ; A P c : 6 é : : : Bl Blind and Cave Sere rates and fee Byes ; : . : 3 : c : ue Mammals . : : : : . : : : 2 5 : : é 5 5 92} Eyes of the Common Mole a : : é é . : : : : : : 5 2

The Cave Rat and its Eyes : : . : : : : : é : : : 54 0)

The Cave Salamanders”. 6 . é : : : yee : : 5 2S

The eyes of Zyphlomolge GED 3 0 : c ; : é . : : : esr

Sclera and Choroid . 5 : ; : 2 c : : e : 2

Pigment Layer Exclusive of the Teidieal Parts ¢ 5 : : ; : : 3 + 833)

Iris and Ora Serrata . : 7 - - : 4 9 3 " : 3 . ass

The Retina . : : : é : : : : : C 35

The eyes of Zyfhlotriton ape Seejneces 5 : : : : 9 : : , - 36

Conclusions as to the eye of Zyphlotriton speleus . 5 : 5 9 : : . + 40 Summary in regard to 7yfhlotriton . . ¢ : : 5 : : 9 : . - 4!i

The Blind Reptiles. a . 5 5 é : : : o : : 5 ; : ohn 42

Amphisbena punctata 5 : 5 : : : . : 5 5 eA

Methods. c ; 5 ; 5 4 : ; ; 5 : c ee 42

General Account of the Bye. : 5 2 : : : c ; z : : 2

Minute Anatomy of the Eye é : : : : ; : : : ; é a4

Rhineura floridana . 5 : : : : 2 < é : § < ; 5 5 ks}

Habits of RAzneura . A i : , 5 5 5 : 5 - 48

General Account of the Byel of Te ee : : > . : ; : : : - 49

Minute Anatomy of the Eye of Rizneura . 3 c : ; : : : : - 50

Typhlops lumbricalis . 3 ; : : : : 6 c 5 : sa

General Account of the Byes of Snakes : : . 2 : : : < : > 54

Eyes of Zyphlops vermicularis. 3 : : : : 3 ; ; : : - 55

Eyes of Zyphlops lumbricalis . . 5 5 : : : : : 9 ¢ 50)

Conclusions as to the eyes of Blind Reptiles : : : 5 ; : : : : 59

Amphisbena . : : : : : ; : 5 c 4 . 3 59

Rhineura . : 3 : : : : : : 2 5 : 5 : o Le

Typhlops . : : : : é c ; : 5 : ; : Go

Eyes of Cyclostome polistotrema stot : . é : : ; : : : ; : = | 6

Fishes : : . : : : : - A 6 c : = Gz

General Remarks on the bye of Fishes : © : 5 : c : c ; ; > 62

The eyes of Zygonectes notatus . : : A ; : : : - 64

Typhlogobius : The Point Loma Blind Fish andi its Relatives é 5 : : A - =) 65

The Eyes of the Blind Catfish, Ameturus nigrilabris . : : ¢ 5 ‘5 : 5 - 69

lil

lv CONTENTS.

Fishes continued Pace The Amblyopsidz ; 3 3 y iy 5 : Fi 7 “FO Relationships of the eae onside . * . ; : 5 : : : aD ee7fe) Distribution of the Amblyopside : : 3 5 : : 5 5 : : Ae Ai Amblyopsis speleus 5 ; : : c 5 ; 5 ; : ; c eyh! Lroglichthys rose . 5 - : c : 5 : ; 7 : : : 72 Typhlichthys : : 3 ; é 7 : : F 3 : : . 2 Typhlichthys subterraneus . : . : : : 3 : : : . Ye} Typhlichthys osborni . : : : : : d : 2 ; : - - 74 Typhlichthys wyandotte : : é : 3 3 : : 5 0 : ae 75 Chologaster cornutus . ; : ‘5 ; : é : : : c ; ot As Chologaster papilliferus ¢ : 7 c ' : : : 3 0 é 75 Chologaster agassizit . : : - 5 : : : : - : 5 7) 76

The color of the Amblyopside . : : : , : 3 : : 5 : - 76 General habits of Amédlyopsis —. : : : : 5 ; : : C 5 a £6) Respiration . : : : : = : : : : : : . ts Feeding habits of Anbbohcs 3 : : . : : E ¢ : : 2) Sk Habits of Chologaster . ; 2 ; : : : ¢ : 5 c es é SEOs Reactions to Light. : : ; : : : . : : : : Sa 187 Breeding habits of Amblyopszs . : : 3 : : : < : eeeG2 Rivalry of Males and Secondary Sora Dieeencee ; : : : 5 : : : 3293 The Egg and General Development of Amblyopsis . A : : A 5 é : 04 The Migration of the Anus : F A , c : ; F i ; é 32.595) The Tactile Organs. : : : : : : : : 5 . , : E - ‘96 The Ear of Amblyopsis 2 : : . : : : : : * 5 - Ico Does Amblyopsis hear”? : : : , : : - : : - : : - 102 The Brain of Amédlyopsis . : : : 5 2 : . : : ; i - 106 Conclusions on the Aniblyopatde : ; é : é é : : : 3 : + 109g The eyes of the Amblyopside . - 5 , , 7 : F : c 4 : A) Chologaster papilliferus : : 7 : co p : : 5 : = = /ELO Chologaster agassizit . : ; ¢ A 2 : a : = 2 3 c + E16 Chologaster cornutus . : é : : : 3 A : : - SeeLI7. Typhiichthys subterraneus . : : . a : ¢ E 5 - 120 Troglichthys ros@ f A 3 A é : : : 5 : é = 126 Amblyopsis speleus . : A 6 : 5 : . c 5 > 134 Summary of the Eyes of the anionic : : : é c = é on 14s Development and Later History of the Eye of Aabiiebses 5 é ; 2 : : : 2 LA7, Growth of the Eye from Time of its Appearance . : ; : 5 ; - é ~ 257 History of the Lens. E : : c : a : . : c : : - 158 History of the Scleral Cartilages . : : : : : : : ; : ; = 158 History of the Optic Nerve . : 5 c 5 : - 159 History of the Development, Maturity, a Deeeeeuan of the Eye : 3 - 160 Comparative Rate of Ontogenetic and Phylogenetic Degeneration of the parts of the Eye - 164 The Future of the Eye : : 5 4 - 166 Retardation and Cutting off of re ey of he Devedapmnent Gh the Eye : : : - 166 Causes of Retardation and Cessation in the Development of the Eye . é : : 2 167; The Eyes of Amédlyopsis and the law of Biogenesis —. : : A : : - 170 Conclusion . A 5 A E a é : a A173 General Summarial Aeedant of the eyes of the Aniblvopeide ; 3 é ; 4 : 2 175 Phyletic Degeneration of the eye of the Amblyopside . : 75 Results of Phyletic Degeneration on the Different Parts of the Eyes of the Acai aecides eel77, Ontogenetic Degeneration . F ; : ; : : . 180 Plan and Process of Phyletic Degcreatiens in ite. Ambion : : : : é . 180

The Cuban Blind Fishes . : : - : : : : : F : ; < : - 183 History of the Work . : : ; : 5 . : . ELS Zoological position of Stygicola and urea : : : : c : > 3 2187 Primary and Secondary Sexual Characters . : : 3 é 5 : 5 c Si iSy

Distribution of Stygzcola and Lucifuga : : 3 : é : = : > - 188

CONTENTS.

The Cuban Blind Fishes continued Nature of the Habitat of Stygécola and Lucifuga . Abundance of S¢ygzcola and Lucifuga . Origin of the Cuban Blind Fishes Physical environment of Stygzcola and ba a and their Reactiong to it Biological environment of Stygzcola and Lucifuga General habits of Luczfuga and Stygicola Breeding habits of Luczfuga and Stygicola The Ovaries of Lucifuga and Sty, es The Eyes of Lucifuga The Eyes of Stygicola On the Ovary and Ova in iar aud Sygcole Conclusions in Regard to Luczfuga and Stygicola The causes of Individual and Phyletic Degeneration .

Frontispiece.

Plate A. Is

NON ND mw moot NF OO ON AM HW NH O

bw NHN NN ON Amn & WwW

iS} xe)

CPW AX EYES

MISE .Or shi Adwes.:

Entrance to Ariguanabo River, Cuba. Blind-fish rocks at base of Point Loma, San Diego, California

Twin and Shawnee Caves

Chologaster papilliferus, S, deler pies seiiaticaneda Splerbs ssnagr Zz iad Zypletrito Speleus ¢

Spelerpes longicauda ana Typhiomolge juhbune

Rhineura floridana

Eye of Zyphlops Pere

Amblyopsis .

Chologaster agassizit, ve Payne r0S@, penal Typhlichth Lys nee aneus

Views of Améblyopsis, early stages : : 5

Tactile organs of Améblyopsis and Chebeeser

Heads of Zygonectes notatus, Chologaster agassiztt, C: Rotazaster papilifors, Zyphichtys subterraneus, Troglichthys rose, and Amblyopsis speleus é é

Photographs of the eyes of Amblyopsis and Troglichthys

. Carboneria Beach near Matanzas. Cave of the Insurrectos, near the Gabonen : . Young of Lucifuga in Ashton Cave. Cave Isabella, showing roots

. Stygicola. (Preserved specimens)

. Living Stygicolas

. Views of Lucifuga :

- Sections of eye of Lucifuga .

. Two sections through right eye er gee. ; . Sections of eye of Luczfuga, showing contents of lens, its aad ire ers Bf retina . Eyes of Luczfuga, showing pigment layer and retina and folding of sclera

. Eyes of Lucifuga, showing differences in size and structure .

. Sections through left and right eye-cavities of Lucifuga

. Sections of eyes of Luczfuga, showing eae layer and cells and ebtace: aaah rectus

muscles

. Eye of old Luczfuga, Stoves SCG mass tend apes nebrone bout eye . Eye of Lucifuga . -

. Eye of Stygicolas and Luc ee :

. Eye of Stygicola .

. Ovaries of Luctfuga and Stygicoa

. Sections of ovaries :

- Sections of ovaries

FACING PAGE

. Title

6

12 28 48 54 70 72

NN NNN NN WWW NRHN ew NNN NNN AGA

N

~

KEY TO DESCRIPTION.OF PLATES AND TEXT FIGURES:

1. Pigment epithelium.

pi. Densest pigmented section of the pigment epithe-

lium, just below the nucleus. . Rods and cones. . Outer nuclear layer. Outer reticular layer. Horizontal cells. Inner nuclear layer. Spongioblastic layer. . Inner reticular layer. . Ganglionic layer. . Optic-fiber layer. a, 0, Ophthalmic artery, am, Ameloid bodies of the pigment epithelium. 4, Brille. bac. Rod. ct. p. Ciliary process. cj. Conjunctiva, cj. s. Conjunctival sac. chr, or cha, Choroid. chr. 1, Choroidal lymph. chr. f. Choroidal fissure. en. Cones. cn. nl, Cone nuclei. cor. or crn, Cornea.

OD ONIONS U ND

cps. or cpl. sng. Blood-corpuscles in normal vessels.

cps. s. Stagnant blood-corpuscles. d. Dorsal aspect of eye.

dr, Dermis.

e. m. End member of cone,

F. cj. Fornix conjunctiva.

jr. ol, Olfactory pit.

ha. or kyl. Hyaloid membrane. H. gl. Uarder’s gland.

Iris.

1. Outer layer of iris.

2. Inner layer of iris.

c. Interpolated cells.

Left side of eye.

Z a2 Zz dc ih 21, 22, 23 First, second, and third labial scale.’

vl

dns. or 2. Lens.

2. c. Lens capsule.

M. Miillerian nuclei.

m. m. Middle member of cone.

msc. or mu, Eye muscle.

ni. Nucleus.

nl. con. Cone nuclei.

nl. f. Nuclear fragments.

nl. g. Nuclei of the ganglionic cells,

ni. 1. or ni.) Elongate nuclei of the pars ciliaris.

nl, Muet. Miillerian nuclei.

n. op, Optic nerve.

n. s. Nasal scale.

oc. Eye.

o.¢c. Ocular scale,

o. f. Orbital fat.

o. Ss. Ocular scale.

of, Otolith.

p. Pupil.

p. i. Palpabra inferior.

p. Ss. Palpabra superior.

ji. s. Pigment appearing in optic cavity with senes- cence.

pt. sph. Pigment spheres.

p. 4. Pigment layer.

po. s. Preocular scale.

pr. nl, Processes of the cone nuclei.

pupl. Pupil.

y. Right side or retina,

ry. or rt. Retina.

ro. Rostral.

scl. Sclera.

sel. c. Scleral cartilage.

subo, or sb, orb, Suborbital.

v. Ventral aspect.

vit. Vitreous body.

x. Flattened cells beneath pigmented layer, of doubt- ful significance,

y. Flattened cells beneath inner nuclear layer, of doubtful significance,

PREFACE.

INTRODUCTORY.

A cave is a unit of environment so well circumscribed and of such simplicity that we may know its contents, its elements, and its conditions nearly as well as the experimental zoologist knows the contents and conditions of his aquarium. These contents and conditions are of rare uniformity, changing but little from day to night, from season to season, or from decade to decade. The point of chief interest in the cave environment is the total absence of light in all parts except about its mouth. Probably no animals have a more intimate environmental adaptation than those inhabiting caves. This adaptation is largely of color and structure of eye, which modifications are surpassed only by the functional adapta- tion of the tactile apparatus of the blind forms.

While no one has followed, and although we may not be able to follow in detail, the steps through which the cave animal has acquired this environmental adaptation, a knowledge of the present condition of their unchanging environment gives us a knowledge of what it has been during their entire period of development.

We know, or can know, what the present stage of their adaptation is. Not in- frequently we know what the condition of the animal was at the start of its cave experiences and enough of the steps along its line of evolution (indicated by the degrees of adaptation reached by different members of the group) to enable us to form so clear a picture of its entire route of evolution that we may conjecture what elements of the environment caused the modifications, and by what process they were brought about. We have, in other words, a long experiment conducted by nature unrolled before us.

I propose in this work to give an account of the cave as an environment ; to bring together in a revised form the papers on blind and cave vertebrate animals so far published by myself and my students, together with further observations on the species previously considered, to consider the habitat, mode of life, and the origin of the Cuban blind fishes, and to give an account of their eyes.

My first experience with blind vertebrates was in 1886, when Superintendent Funk sent to Indiana University a living blind fish which had been taken from a well at Corydon, Indiana, and which proved to be a new species, T'yphlichthys wyandotte, the only representative of the genus so far taken north of the Ohio River. Later, when a stay in southern California came in prospect, a study of the blind fish, T'yphlogobius, living under rocks along the base of Point Loma, was one of the first definite plans formed.

When, in 1890, I returned to Indiana and was once more within reach of the caves, the problem again came up. My laboratory is excellently located for the study of cave faunas, the series of caves to which Wyandotte, Marengo, Mammoth,

vii

viii PREFACE.

Colossal, and Nickajack belong, beginning in or about the campus of Indiana University. But while seemingly ideally located, and in spite of the fact that numerous trips were made to Indiana caves, especially those from which blind fishes had been reported, no blind fishes were found till 1896.

In May, 1896, I was again looking for blind fishes east of Mitchell, Indiana, this region being drained by underground streams. East of Mitchell several of these find their exit in caves of romantic beauty in the escarpment flanking the valley of White River (plate A). The roof over one of the streams has fallen in at two places, Dalton’s Spring and Twin Caves. At Dalton’s Spring the cave-stream runs above ground for about too yards when it again enters its subterranean course. Within sight of the lower opening of the “spring” I saw two blind fishes swimming in a quiet pool. I secured about 20 specimens and had found the stream which in its varying reaches has furnished me with an unlimited supply of specimens which have enabled me to give the complete history of the eye of this species, Amblyopsis speleus De Kay. More material has been obtained from this cave than from all others put together. In 1903 the State legislature of Indiana placed the land, about 182 acres, on which are the entrances and exits to this stream in the keeping of the trustees of Indiana University. While some litigation has arisen as to the ownership of the farm, it will probably be permanently preserved as a State park.

ACKNOWLEDGMENTS.

Through grants from the Elizabeth Thompson Science Fund and from the American Association for the Advancement of Science I have been able to visit the cave regions of southwestern Missouri, about San Marcos, Texas, Corydon, Indiana, and Mammoth Cave, Kentucky. In 1902, through a grant from the American Association for the Advancement of Science and assistance from various other sources, I was able to visit the blind-fish caves of Cuba. Subsequently the Carnegie Institution of Washington aided me in making additional investiga- tions in Cuba. The part of the present volume dealing with Stygicola and Lucifuga is my final report on the work carried on with this aid, and in it a detailed account of the Cuban work is given.

Prof. S. A. Forbes kindly lent the drawing for figure A, plate 1. The draw- ings of sections of eyes were made under my direction by Mrs. E. R. Bieling in the laboratory of Prof. R. Wiedersheim, in the University of Freiburg, Germany, and I am indebted to Professor Wiedersheim for placing his laboratory at my disposal.

I am under many obligations to various friends, both at home and in Cuba. Mr. Oscar Riddle, Dr. John Beede, Mr. John Haseman, Mr. Norman MclIndoo, and Mr. T. L. Hankinson acted as volunteer assistants on various Cuban trips, always working without remuneration and in part paying their own expenses. The late Prof. Jose T. Torralbas, Prof. Carlos de la Torre, Mr. Pascual Ferreiro, Dr. Felix Garcia, and the Director of the Cuban Agricultural Station, Prof. F. S. Earl, assisted me materially in various ways.

The assistance of my friend, Mr. Francesco Martinez, has been invaluable. His finca, the “Isabella,” is at the margin of the cave region of Cuba, and in the interval between our trips he ferreted out unsuspected caves, determined their rich- ness in blind fishes, and put himself at our disposal in guiding us to his various finds.

Prof. D. W. Dennis of Earlham College, Richmond, Indiana, made the micro- photographs in a manner to leave nothing desired (plates 9, 10, 16-23).

PREFACE. ix

Mr. Lewis H. Wild, under the direction of Prof. J. Reighard, made a series of photographs of entire eggs and embryos (plate 7).

Mr. Samuel Garman sent me my first specimens of the blind fish, Troglichthys.

Dr. B. W. Evermann of the Bureau of Fisheries and the late Prof. W. Norman secured me specimens of T'yphlomolge.

Prof. Wm. Roux, Dr. F. R. Lillie, and others kindly consented to the repub- lication of articles issued in the journals under their editorship.

I desire also to express my high appreciation of the interest taken by the authori- ties of Indiana University, especially by President William Lowe Bryan, in the various trips and plans necessary to bring this work to a successful conclusion.

The present work forms No. 97 of the Contributions from the Zoological Lab- oratory of the Indiana University.

Finally, I wish to express my indebtedness to her who as Rosa Smith guided me to the blind-fish rocks at the base of Point Loma, and who as Mrs. R. S. Eigen- mann collected for me at the same place, has acted as editor of the various papers that have appeared, and through the twelve years during which my leisure has largely gone to the blind vertebrates has ever been ready with advice, encour- agement, and assistance.

CONCLUSIONS OF GENERAL IMPORT.

(t) The bleached condition of animals living in the dark, an individual envi- ronmental adaptation, is transmissible and finally becomes hereditarily fixed. (See page 8o.)

(2) Ornamental secondary sexual characters not being found in blind fishes are, when present, probably due to visual selection. (See page 94.)

(3) Individual degeneration of the eye may begin in even earlier stages of development until nearly the entire development becomes affected, that is, func- tional adaptations are transmissible. (See pages 172 and 235.)

A GENERAL CONSIDERATION OF CAVES AND THE CAVE FAUNA

CAVES AND, THE CAVE FAUNA.

CAVES IN THEIR RELATIONS TO THE REST OF THE UNIVERSE.

The environment favorable to animal life is limited to a thin layer of water, earth, and air. From its deepest to its most elevated point this layer does not much exceed to miles‘ in thickness. At no particular point does it exceed much more than half this thickness; and usually the layer is but a few feet thick. About half the total thickness is below sea-level and the other half above it. ‘The places where the ocean has a depth of 5 miles are few, but in these places the greatest depth of possible environment is found. The favorableness of the environment diminishes rapidly with the depth. The depth of the possible environment at any point on land above the surface is very limited, and beneath the surface it depends on conditions; solid rocks may limit it to the surface and soil may permit mam- mals, and especially insects, to burrow several feet beneath the surface. Under- ground watercourses, which are caves in the formation, may enable animals to live several hundred feet beneath the surface of the ground. The animals thrown out by artesian wells attest this. Zyphlomolge is occasionally thrown out of the artesian well 190 feet deep at San Marcos, Texas. ‘The plant environment stops at the surface of the ground; * animal life diminishes rapidly within a few feet of the surface unless trees cover the ground. Animal environment definitely stops at the tops of trees, though the air above them may be temporarily visited.

While the depth of the environment at any point is only a few feet on land, because the surface of the land itself rises to a few miles above sea-level, the total depth of the environment above sea-level is considerable. The fauna rapidly diminishes in either direction from sea-level, and were it not that the extreme limits of the environment, above and below, furnish rare, sometimes peculiarly adapted forms, sometimes relicts, the numbers of individuals and types found would not repay the exploration of the ocean depths and mountain heights.

Since the environment varies within the limits of the possible existence of living matter, from the extreme of wetness and dryness, of heat and cold, of depth and height, of light and dark, etc., we may divide the environment into many distinct units within which the conditions are similar or alike. It is profitable at present to call attention only to discontinuous and continuous units of environment. Similar or identical conditions may stretch uninterruptedly in one or more directions indefi- nitely, permitting the free movement of its inhabitants from one part to another. The continuous unit of environment of greatest extent is furnished by the ocean at considerable depths. Light and temperature conditions and seasonal fluctuations are reduced to the minimum and are nearly uniform under the whole surface of the ocean, furnishing an ideal of the type of the continuous environment. This particular environment is continuous not only as to space, but also as to time.

The surface of the ocean forms an equally continuous area, but because tem- perature and light conditions differ greatly in different parts of the globe we must here deal not with a single but with several distinct units of environment, each large in extent. If we assume the conditions in the north polar sea to be identical with

Highest mountain, deepest ocean. * Some fungi are found in caves.

3

4 BLIND VERTEBRATES AND THEIR EYES.

those of the south polar sea, these form a discontinuous unit of environment, a unit whose parts do not form a portion of a continuous area and whose inhabitants can not migrate from one part to the other.

If we assume the conditions in the equatorial Atlantic to be the same as those of the equatorial Pacific, we are again dealing with a discontinuous unit —discontinuous because the inhabitants of one part can not migrate to the other. If we examine these two units more closely, it becomes evident that the Arctic and Antarctic oceans have always formed a discontinuous unit. Arctic conditions have never prevailed between the two. On the other hand, the equatorial Atlantic and the equatorial Pacific were formerly connected in Colombia and formed one continu- ous environment. The land area and the fresh waters near the equator from Para to the Andes form a continuous unit of environment, and the Galapagos Islands to the west of it form a discontinuous unit, each separate island forming a continuous unit of a smaller order. It is evident that there are degrees of discon- tinuity, depending in part on the length of time the discontinuity has existed, and in part on the space separating the nearest parts of the unit.

Caves are discontinuous units of environment whose elements have always been separate. It is possible that in some areas a large complex of different under- ground channels exists. An east to west fault has lowered the southern part of Texas, or has raised the northern part, many feet. The dividing line is an abrupt escarpment across the State. This fault has favored the formation of underground watercourses, and inasmuch as river valleys do not cut down to the underground channels, it is possible that they form a network of channels or a continuous unit which permits the ready migration of its inhabitants from one part to another.

The lower area on the southern slope of Cuba, between Cafias on the west and an undetermined point east of Union, is drained by underground rivers. No valleys cut down to these rivers, and since this part of Cuba has sunk in recent times, the land being only a few feet above sea-level, it is possible that we again have a complex of underground channels permitting the migration of its inhabit- ants. However, it is also possible that the streams run in separate courses. ‘The absence of Lucifuga from the eastern caves favors this hypothesis. At best we have here several degrees of continuity.

The large streams cut the cave region of Kentucky, Indiana, and Missouri into sections, their beds lying deeper than the caves. These caves are, therefore, part of a discontinuous environment. ‘These facts must be constantly borne in mind in considering the origin and dispersal of cave faunas.

It is quite out of the question in this connection to give even a partial list of North American caves, or an account of the North American cave regions. The region to which Mammoth Cave belongs reaches from near Bloomington, Indiana, through Kentucky into Tennessee and embraces many thousand square miles of territory. Only the larger streams whose rapidly deepening channels have made the caves possible flow on the surface. ‘‘One may travel on horseback all day, through certain parts of Kentucky, without crossing a single running stream; all the rain water that falls being carried down through the sink holes into caverns below where are the gathering beds that feed the few large open streams of the region, of which Green River is an example. It is reported that there are 4,000 sink holes and 500 known caverns in Edmondson County (Kentucky) alone.” *

' For an account of the principal caves of North America see Hovey, Celebrated American Caverns, Cin- cinnati, 1882 and 1896; and Packard, The Cave Fauna of North America, Memoirs of the Nat. Acad. Sci. vol. 4, 1888.

or

CAVE ENVIRONMENT.

THE NATURE OF THE CAVE ENVIRONMENT.

Each cave is a distinct unit of environment and needs special consideration. In the present work we can deal only with the general features of this environment. The chief element for consideration is the absence or reduction of the amount of light and the relative constancy of other physical conditions. On this basis a cave may be divided into three regions: (1) the twilight region just within the cave, bounded by the distance to which light penetrates from without this part shades generally from epigean conditions to the real cave conditions; (2) the region of fluctuating temperatures; (3) the inner cave region.

These different sections occupy greatly variable parts of different caves. In Mammoth Cave the twilight region is large enough to contain a tennis court and reaches some distance beyond the “‘iron door.””? Some Cuban caves are entirely of the twilight character, usually containing an abundant fauna, consisting largely of occasional, regular, or accidental visitors from the outside. The second region in Mammoth Cave reaches to the Mammoth Dome. On a cold winter day I found ice stalagmites on the floor of the entrance gallery just before it enters the dome. In certain of the ice caves the entire portion beyond the twilight area may belong to this section. In caves of the tropics, on the other hand, it may not exist at all. The third part is the cave par excellence —the inner section, but little influenced by external conditions. Here there is absolute darkness at all times, both day and night, summer and winter following each other without very decided change in temperature.

The temperature differs in the various parts of the same cave and also changes slightly with the seasons. In the center of the Shawnee Cave at Mitchell the fluc- tuations in temperature during a week do not equal the error of the recording ther- mograph arising from unequal trimming of the paper, the absorption of water, etc. The total fluctuation during a year is 2.2° C. It is remarkable that this record of cave temperature is taken in a cave open at both ends with a current of air flowing through it at times. The instrument is placed where it would be least affected by these currents, that is, in a large room near the center of the cave about 15 feet above water-level.

Glaciéres, or ice caves, are found in various places. ‘They exist wherever the prevailing direction of the winds and nature of the cave causes a strong inflow of air during the winter, reducing the temperature to below the freezing point. ‘The summer winds do not blow in the same direction, and convection currents are pre- vented by the nature of the cave."

Between June, 1906, and February, 1908, the fluctuations in the temperature in the water where it leaves Shawnee Cave ranged from a maximum of 17.3° C. to 7.4°, or through about ro° C.’

1 A very extensive list and excellent account of glaciéres is given by Balch in his Glaciéres or Freezing Caverns, 1g00. Concerning the cause of glacitres, he says, on page 148: “The cold air of winter sinks into and permeates the cave, and in course of time freezes up all the water which, in the shape of melting snow or cold winter rain or spring water, finds its way in; and once ice is formed it remains long after ice in the surrounding open country has melted away, because heat penetrates with difficulty into the cave.”

2 This range becomes interesting when compared with the range of temperatures in a lake. Professor Birge gives the ranges of the water at the surface and at the depth of 18 m. for Lake Mendota:

Surface, 1895 . . . to 24° Bottom, 1895 . . . 1.5° to 17.1° Surface, 1896 . . . to 26° Bottom, 1896... to 16°

6 BLIND VERTEBRATES AND. THEIR EYES.

Conditions of moisture, while practically uniform in some parts of caves, fluc- tuate in others more than any other element of environment. The maximum degree of moisture is naturally found in the pools and streams. On the other hand, in the upper parts of Mammoth and Wyandotte Caves the dust lies undisturbed for years. In Mammoth Cave the tracks of oxen made in 1860 are now shown to visitors, and I am told that in Wyandotte the still older tracks of the moccasined Indians are perceptible to-day. There are, however, parts of caves where the moisture dripping through from above is considerably increased after a rain, and the River Styx in Mammoth Cave rises 60 feet above low-water mark. The creek in Shawnee Cave sometimes fills parts of the cave to the ceiling.

The conditions of the water also change very greatly. At ordinary times it may be very clear; after rain it may carry a large amount of sediment. In its low condition it may flow very quietly, in its high condition be a torrent. The water, then, fluctuates in amount, clearness, and swiftness, with meteoric conditions.

Charts of simultaneous records on two self-registering barometers show the close agreement in changing barometric pressures inside a cave and outside it. One of the instruments was placed about go feet above the exit of the cave, the other near the middle of Shawnee Cave. Records chosen on account of peculiarities in the rise and fall of the pressure at certain times leave no room for doubt that baro- metric changes similar to those of the outside take place in the caves.

The following table shows the temperatures for air and water in Donaldson and Shawnee Caves in 1906 and 1907:

Temperatures for air and water in Donaldson and Shawnee Caves.

Maximum Maximum i | Maximum Tempera- | tempera- Tempera- | tempera- Minimum Tempera- | tempera- | Eee ; ture of air) ture of | ture of air} ture of “tempera- ture of air} ture of tempera- Time. _|in center of|water at its| Time. in center of|water at its! “(ure at Time. in center of|water at its) “ture at | Donaldson| exit from |} Donaldson} exit from ein Donaldson) exit from anne | . Cave. Shawnee Cave. Shawnee SFiS Cave. Shawnee place } Cave. Cave. bgt | | Cave. cae eves te = a | a aa = a 4 == =f Se 1goo. 1907. 1907. | rulyeeerrs 12.7 12.4 Webstore iy 01.67 9:5," ||| Julyce.e.| “sortor || =eeced Sc August... 9 12.5 Feb.=-- 11.5 et. 3 8.9 || August...} 12.7 16.4 | 13.1 September) 13.2 12.6 March..| 11.5 12.6 9.9 September] 12.7 723 al LS | October - . iad |\pealene a | April.-.:|(< 2i55 I2.I | 10.2 |} October.-| 12.2 13.4 T203 November! 11 10.3 May.-..] 1.5 12.8 | -x1.6 November] 11.9 rey le ara December] 12.2 | Io. | June.... DIT. 15.1 12.5 || December} 11.7 L2.0 7.4

* The higher temperatures are caused by rains and last only a few hours after a heavy rain. During the first 10 days in September, 1907, the temperature of the water was 14.5, 15.6, 17.3, 16, 14.0, 14.6, 13-9, and 15.3 on successive days. During the last 10 days of the month it ranged from, 15? to 15.5