54 



HARDWICKE'S SCIENCE-GOSSIP. 



THE BLIND PISHES OF THE KENTUCKY 

 MAMMOTH CAVE. 



WHATEVER value in itself the Darwiuiau 

 theory of "Natural Selection" may pos- 

 sess, there can be no doubt that its promulgation 

 has given a marvellous impetus to natural science. 

 Many of the views taken in connection with it have 

 enabled us to understand certain phenomena which 

 before were inexplicable. Chief among these may 

 be mentioned the doctrine of retrogradation. It is 

 a mistake to suppose that the Darwinian theory 

 countenances progression only — it endeavours, also, 

 to explain degradation. Thus, on certain islands 

 the beetles are wingless, although nearly allied to 

 species in which the wings are well developed. 

 This is explainable on the ground that on islands 

 where the sea and land breezes blew strong, the 

 beetles best gifted with powers of flight would be 

 the first to suffer, would be carried seawards, and 

 perish; whilst the weakest-winged beetles would 

 stand the best chance of remaining behind, and of 

 stocking such islands with beetles that would 

 certainly inherit what would have been elsewhere a 

 defect in their parents, but which thus turned out 

 to be the means of the perpetuation of the race. 



or semi-developed condition. The "Cat-fish," 

 family {Sllurida) is interesting to naturalists on 

 account of the singuhir and diversified arrange luent 

 and position of the eyes of its members, which are 

 thus enabled to adapt tliemselves to a variety of 

 physical conditions such as are not so largely shared 

 by any other fishes. As regards the degree of 

 optical development, also, the eyes of the various 

 species are very peculiar. They range from partial 

 and even total blindness to perfect sight ; and are 

 placed in every possible position about the head. 

 The blind members of this group, however, seem to 

 inhabit subterranean streams, one species, taken in 

 the Conestoga river, Pennsylvania, having its eyes 

 quite rudimentary. This species was believed to 

 have found its way into the river from the subter- 

 ranean streams which are known to empty them- 

 selves into it. 



The most striking feature about the appearance 

 of the blind fishes of the " Mammoth" cave is their 

 want of colour. This alone would indicate the 

 length of time during which they have existed out 

 of the light; whilst the darker shades of blind 

 fishes in other caverns equally point to a shorter 

 period during which the species has been exiled into 

 darkness. We mentioned in a zoological paragraph 

 last mouth, the various animals inhabiting this re- 



Fig:. 35. Amblyopsis spel<£vs, nat. size. 



This law of retrogradation, operating whenever 

 it is of advantage to the species operated upon, is, 

 perhaps, still better illustrated by the occurrence 

 in ancient caverns and subterranean rivers of 

 animals wholly or partially blind, which are never- 

 theless closely related to neighbouring species in 

 which the sight is in its normal condition. The 

 fishes of the celebrated "Mammoth" cave in Ken- 

 tucky have long been known to naturalists, and 

 regarded as curious freaks, rather than as illustra- 

 tive of the operation, of an important natural law. 

 The natural history of these fishes, and their rela- 

 tions to others of the piscine tribe which are found 

 occupying similar habitats elsewhere, have been care- 

 fully and elaborately treated upon by Professor 

 Putnam, in the American Naturalist for January 

 last. As is well known, we have fishes existing, 

 such as tlic Lancelet, in which not only the eye but 

 the entire nervous system is in a very nidimentary 



markable cave, which were in a similar state of 

 blindness ; so that the limited subterranean fauna is 

 very interesting, as showing the effects of conditions 

 of life, not only on exterior form, but also on in- 

 ternal structure. The blind fish from this cave, 

 longest known to naturalists, is Amhhjopsis spe- 

 hcus (fig. 35), a name which indicates both its de- 

 fective vision and subterranean habitat. The eyes 

 of this fish are quite rudimentary ; but to make up 

 for this defect the head is covered with a number 

 of papilla;, or organs of touch, which the numerous 

 fine nerves leading to them indicate must b.c of a 

 very highly developed character. The nearest allies 

 of the Amlthjopsis are the Mimiows. How well the 

 sense of touch serves it is best shown by the fact 

 that smaller fish, upon which it fed, have been 

 found in its stomach. It is probable that the move- 

 ment of its prey in the wafer iuQuenced the delicate 

 tactile organs so as to enable it to follow the prey 



