MUSEUM OF COiMPAUATIVE ZOOLOGY. 79 



distinct nucleus ; 4th, just in front of the globe a lenticular-shaped, 

 transparent body, which consisted of an external membrane containing 

 numerous cells with nuclei." The pigment layer he regards as repre- 

 senting the choroid, and the layer of colorless cells within — and it 

 should be particularly noticed that it is according to both his descrip- 

 tion and figures a single layer — as representing the retina. It is 

 very desirable, indeed, that these eyes should be studied anew with 

 modern methods of preservation and by means of sections ; for, if 

 Wyman's account of the structure proves to be correct, we have here a 

 most interesting deviation from the three forms best known and already 

 compared. It may be supposed that his statement concerning the 

 cellular condition of the lens is correct ; for this involves merely the ob- 

 servation that a given structure is composed of cells, while his state- 

 ment concealing the retina involves an observation as to how the cells 

 in a given cellular structure are disposed, — two quite different matters, 

 as every histologist knows. In this particular the lens of Amblyopsis 

 corresponds, then, to that of Talpa ; but in the latter animal the retina 

 is fairly well differentiated, and even in Proteus, where the lens is 

 wholly wanting in the adult, the retina is differentiated to a consider- 

 able extent. If Wyman is correct in supposing that the retina in Am- 

 blyopsis is represented by a single layer of cells, then we have a 

 condition corresponding more nearly to that found in Myxine than in 

 any other known vertebrate, although even here the retina proper is 

 far from being a single cell layer, but the eye of this latter form has no 

 trace of a lens. 



Cope ('64, p. 232) remarks with regard to the blind Silurid, Gronias 

 nigrilabris, that in no case has he found anything representing the lens. 

 Whether a considerable number of specimens were examined with refer- 

 ence to this point, the author does not state ; but from the general char- 

 acter of the fish and its eyes, as described, it appears to me quite probable 

 that, as Packard suggests, further examination will lead to the discovery 

 that the lens is not entirely absent. 



I cannot refrain from saying at this point a few words on the ques- 

 tion which, in reality, induced me to undertake the study of the eye of 

 Typhlogobius, viz. the question of the actual degeneration of function- 

 less organs. There is a belief prevalent among zoologists, though to 

 just what extent I am unable to say, that, if a structure undergoes de- 

 generation in ontogeny it does so in the reverse order of its pliylogeny. 

 It would appear that a degenerating vertebrate eye with its great com- 

 plexity of organization, this complexity having been taken on by degrees 



