246 



NATURE 



{July 25,1872 



THE BLIND FISHES OF THE MAMMOTH 

 CAVE AND THEIR ALLIES* 



THE blind fish of the Mammoth Cave has from its 

 discovery been regarded with curiosity by all who 

 have heard of its existence, while anatomists and phy- 

 siologists have considered it as one of those sin<riilar 

 animals whose special anatomy must be studied in order 

 to understand correctly facts that have been demonstrated 

 from other sources ; and, in these days of the Darwinian 

 and development theories, the little blind fish is called 

 forth to give its testimony, pro or con. 



Before touchini; upon this point, however, we must call 

 attention to the structure of the fish and its allies, and to 

 others that are either partially or totally blind. 



In the lancclet [BraiiLhiosloiiia) and the hag {Myxiiif) 

 the eye is described " as simple in form as that of a leech, 

 consisting simply of a skin follicle coated by a dark pig- 

 ment, which receives the end of a nerve from the brain." 

 .Such an eye speck as this structure gives would only 

 answer for the simple perception of light. In the youngl' 

 of the lampreys {Pctroniyzon) the eye is \tty small and 

 placed in a fold of the skin of the head, and probably of 

 little use, as these young remain buried in the sand ; but 

 as they attain maturity, and, with it, the parasitic habits 

 of the adult, their eyes are developed to a fair size, thus 

 reversing the general rule in the class. 



In most other fishes the eyes .arc developed to a full and 

 even remarkable extent as to size and perfection of sight 

 in water. In Aiiahlcps, or the so-called four-eyed fish of 

 the fresh waters of Central and South America, which 

 belongs to a closely allied family with our blind fish, the 

 CyprinodoiitidLr, the eyes arc not only fully developed, 

 but are divided into an upper and lower portion in such a 

 way, by an opaque horizontal line, as to give the effect of 

 two pupils, by which the fish probably sees as well when 

 following its prey on the surface with its eyes out of water, 

 as when under water. But it is in the interesting family 

 of Cat fishes {Siluridic) that we find the most singu- 

 lar arrangement of eyes in perfect adaptation to the 

 diversified modes of life of the numerous species. In this 

 family the eyes assume nearly every possible modification 

 from partial and even total blindness to perfectly developed 

 eyes, and these organs are placed in .almost every con- 

 ceivable position in a fish's head ; from the ordinary large 

 eyes on the side, to small ones on top of the head, enabling 

 the fish to see only what is above ; to the oval eyes on the 

 side, in some just back of the mouth, situated in such a 

 way that the fish can only see what is in close proximity 

 to its jaws or even below them. Many genera of this 

 family found in South America, t Africa,§ and Asia,l| have 

 the eyes so small and buried under the skin, or protected 

 by folds or cartilage, as evidently to be of no more use 

 than simply to distinguish light from darkness. 



Among the most interesting forms of this family, in this 

 respect, i« the genus described by Prof. Cope under the 



* Reprinted from the Amcricnn Matiiralist, .1 sequel to '"The Blind 

 Crustacea of the Mammoth Cave." See Nature, vol. v. pp. 445, 434. 



+ These young lampreys have been described under the generic name? oT 

 Ammoc<ttes, and it was not until 1856, when Prof. Miiller discovered the f,ii:t 

 of a metamorphosis in the lampreys, that their true position was ascerlainud- 

 Prof. Miiller has traced the liistory of the common European species. ..nd 

 shown that it is three or four years in attaining its perfect form. With tliis 

 fact before us and with the early stages of the Myxinoids still unknown, have 

 we not some reason for suspecting that the laucelet may yet prove to be a 

 larval form of the Myxinoids, notwithstanding that it is said to lay eggs'/ 

 Why should we not suspect the existence in the very lowest vertebrates of 

 sometliing akin to alternate generations, or of larva; capable of reproduction ? 

 Without having any facts to support such an assumption, except that, on 

 general principles, the young of Myxiiie would probably be very much like 

 Branchiostoma, and that its young is not known, while Branchiostoma has 

 only been found in waters where some species of Myxinoid exists, I think 

 that before the position of the lancelet is firmly established, we must know 

 the embryology of the Myxinoids ; for should the lancelet prove not to be 

 the young of the Myxinoids, it must necessarily form a distinct c-ass of 

 animals, perhaps as near to the molluscs as to the vertebrates. 



X Pimelodus cyclopiiiin of Humboldt, Helogenes, Agoniosus and other 

 genera. 



% Kiiiropius coitgeHsis. 

 \ li Ailia, Shilhiclithys, Bugroities, and other genera. 



name of Gronias jiigrilabris. This fish is very closely 

 allied to our common bull pout or horned pout, and of 

 ,aboutthesamesize(teninchesinlength). It was taken inthe 

 Conestoga river in Lancaster Co., Pennsylvania, where it 

 is " occasionally caught by fishermen and is supposed to 

 issue from a subterranean strcanr said to traverse the 

 limestone in that part of Lancaster Co., and dischar^'e 

 into the Conestoga.'' We quote the following from Prof. 

 Cope's remarks on the fish :* — 



" Two specimens of this fish present an interesting con- 

 dition of tlie rudimcntal eyes. On the left side of both a 

 small perforation exists in the corium, which is closed by 

 the epidermis, representing a rudimental cornea ; on the 

 other the corium is complete. Here the eyeball exists as 

 a very small cartilaginous sphere with thick walls, con- 

 cealed by the muscles and fibrous tissue attached, and 

 filled by a minute nucleus of pigment. On the other the 

 sphere is larger and thinner walled, the thinnest portion 

 adherent to the corneal spot above mentioned ; there is a 

 lining of pigment. It is scarcely collapsed in one, in the 

 other so closely as to give a tripodal section. Here we 

 have an interesting transitional condition in one and the 

 same animal, with regard to a peculiarity which has at 

 the same lime physiological and systematic significance, 

 and is one of the comparatively few cases where the phy- 

 siological appropriateness of a generic modification can 

 be demonstrated. It is therefore not subject to the diffi- 

 culty under which the advocates of natural selection 



Fig. I.— Cuban Blind Fish : Lucifuga subterraneus. 



Labour, when necessitated to explain a structure as being 

 a step in the advance towards, or in the recession from, 

 any iDikiiowii modification needful to the existence of the 

 species. In the present case observation on the species 

 in a state of nature may furnish interesting results. In 

 no specimen has a trace of anything representing the lens 

 been found." 



When we remember that the lens of the eye in Ambly- 

 opsis has been found, even though the eye is less developed 

 in all its parts than in Grmiias,\X. is probable that a careful 

 microscopical examination would show its existence in 

 this genus also. 



It is interesting to note that this fish is black above 

 (lighter on the sides and white below), notwithstanding its 

 supposed subterranean habits, and that all the other 

 members of the family having rudimentary or covered 

 eyes are also d.ark coloured, while the blind fishes of the 

 Mammoth Cave and of the caves in Cuba are nearly 

 colourless. This want of colour in the latter fishes has 

 been considered as due to their subterranean life. If this 

 be the cause, why should the blind cat-fishes retain the 

 colours characteristic of the other members of the family 

 living in open waters ? 



The fishes which in a general way, so far as blindness, 

 tactile sense, and mode ot life are concerned, come the 

 nearest to the blind fishes of the Mammoth Cave, are 

 those described by Prof. Poeyf under the names of Liici- 

 fiiga subterraneus and L. deiitatus.t These fishes having 



^ Proceedings of the Academy of Natur.il Sciences of Philadelphia for 

 1864. p. 231. 



t Memorias sobre la Historia Natural de la Isla de Cuba, por Felipe Poey. 

 Tomo2, pp. 95-114. Pis. 9, 10. II. Habana, 1856-8. 



t This species was afterwards referred to the genus Stygtcohi Gill, on ac- 

 count of the presence of palatine teeth which are wanting in the other spe- 

 cies. There are also .several other good characters, to judge from the figures 

 of the head, skull, and brain given by Poey, that would warrant the refer- 

 ence of the fish to a distinct genus from L. subterraneus. 



