MEiAIOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 133 



afterwards seven more specimens were taken from the same spring. As observed by Professor 

 Forbes, this species " indicates a more advanced stage of adaptation to a subterranean life than 

 that of its congeners. On all the surfaces of the head appear short rows of peculiar tubercles 

 relatively wider than the papillae of A.mblyopsis, but also apparently shorter. They are much the 

 largest about the anterior nostril aud on the lower jaw, and are larger on the side of the head 

 than on its upper surface. While the papillae of Amblyopsis are set on ridges of the skin, those 

 of this Chologaster are somewhat sunken within it, and are often placed in grooves; and it is not 

 uutil they are freed from the adjacent epidermis by dissection that their full height is seen. When 

 thus exposed they closely resemble the papillae of Amblyopsis in form and size and are similarly 

 cupped at the tip." Professor Forbes concludes that the discovery of a species of Chologaster 

 which frequents external waters of an immediately subterranean origin supplies all needed proof 

 that the genus either has a shorter subterranean history than Amblyopsis, or, at any rate, has 

 remained less closely confined to subterranean situations; and that in either case the occurrence 

 of eyes, partial absence of sensory papillae, and persistence of color are thus accounted for con- 

 sistently with the doctrine of " descent with modification." 



Another example of a blind-fish with rudimentary eyes which does not permanently live in 

 total darkness, but occasionally visits well- lighted places, is the Gronias nigrilabris of Cope. It 

 is allied to the common horned pout and about 10 inches in length. It was taken in the Conestoga 

 River, in Lancaster county, Pennsylvania, where it is " occasionally caught by fishermen, and is 

 supposed to issue from a subterranean stream said to traverse the limestone in that part of Lan- 

 caster county and discharge into the Conestoga." 



Professor Cope adds : 



Two specimens of this fish present an interesting condition of the rudimental 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 scarcely collapsed iu one, in the other so closely as to give a tripodal section. Here we have 

 an interesting transitional condition iu one aud the same animal with regard to a peculiarity which has at the same 

 time physiological aud systematic significance, and is one of the comparatively few cases where the physiological 

 appropriateness of a generic modification can be demonstrated. It is therefore not subject to the difficulty under 

 which the advocates of natural selection labor when necessitated to explain a structure as being a step in the advance 

 towards, or in the recession from, any unknown 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. 



THE PROBABLE ORIGIN OF BLIND ABYSSAL ANIMALS. 



As has been observed, no vegetable life occurs in the sea below a depth of 300 to 500 fathoms. 

 What can be the cause of the absence of even the lowest Algae iu the abysses of the ocean, unless 

 it be the absence of light, it is difficult to imagine. In the absence of vegetable life, in the fact 

 that numerous species of animals at the depth of the ocean and in the abysses of fresh-water lakes 

 have either imperfect eyes or uo traces of them whatever, and from the probability that at the 

 depth at which they live there is total darkness, we have an interesting and suggestive parallel to 

 the conditions of cave life. It is most probable that the causes of atrophy or blindness under one 

 set of conditions are the same or nearly the same in the other. 



The proportion of blind or eyeless deep-sea Crustacea to those provided with normal eyes is 

 not as yet exactly known, but the results worked out by Prof. S. I. Smith* regarding the abyssal 

 species of decapod Crustacea dredged by the Albatross in a restricted region of the western North 

 Atlantic may afford an example of what probably obtains for the ocean depths in general. Of 

 forty-four abyssal decapods, twenty-one are enumerated which are supposed to live at or near the 

 bottom. ; 'If we exclude from this examination all the species whose bathymetrical habitat is in 

 any degree doubtful, and examine the twenty-one species given as inhabiting the immediate neigh- 

 borhood of the bottom, we find that Geryon quinquedens, IAthodes agassizii, and Sabinea princeps 



"Annals and Mag. Nat. Hist., March, 1886. 



