15-4 BULLETIN OF THE 



of Newport's paper, to the effect that the eye is " ohne Hornhaut, Pig- 

 ment und Nervenstiibe." The phrase " ohne Hornhaut " means, I be- 

 lieve, that a facetted cornea is not present ; at least this seems to be the 

 interpretation placed on it by Leydig, for the quotation is shortly fol- 

 lowed hy this sentence : " Dort wo man eine gefeldcrte Cornea zu suchen 

 hatte — am Gipfel des Kegels — zeigt sich die Haut von der gewohn- 

 lichen Beschaffenheit." There was greater reason for Leydig's regret 

 that he could not consult Newport's original paper than Leydig himself 

 appreciated ; for, although he probably had no reason to consider the 

 abstract incorrect, if his quotation from it is exact, it differs at least in 

 one respect from Newport's account. Newport described the cornea as 

 facetted ; Leydig's quotation from the abstract states that it was not 

 facetted. I have been unable to discover where this abstract was pub- 

 lished, but, since Leydig quotes directly from it, the probabilities are 

 that the discrepancy between his quotation and Newport's actual state- 

 ment is to be attributed to an error in the abstract. Aside from this 

 difficulty, it must be borne in mind that Leydig and Newport in their 

 observations on the cornea by no means agree ; for while Newport really 

 describes the cornea as facetted, Leydig states from his own observa- 

 tions that it is without facets. According to Leydig, then, the eye of 

 C. peliucidus is more completely degenerated than the observations 

 of Newport would lead one to suppose. 



The latest account of the eyes in blind crayfishes forms a part of 

 Packard's paper on " The Cave Fauna of North America" ('88, pp. 110 

 to 113). Newport and Leydig studied C. peliucidus; Packard had the 

 opportunity of studying not only this species, but also C. hamulatus, 

 Cope and Packard, from Tennessee. In both species according to Pack- 

 ard the cornea was without facets, and the hypodermis was not thick- 

 ened in the retinal region, but an optic nerve and ganglion were present. 

 The results obtained by Packard thus confirm those given by Leydig. 



From this brief historical review it will be observed that one of the 

 principal questions concerning the eyes of blind crayfishes deals with 

 the extent of their degeneration. This change has not only affected the 

 finer structure of the retina, but it has also altered the shape of the 

 optic stalk. I shall therefore begin with a description of the external 

 form of the stalks. 



The optic stalks of blind crayfishes are not only proportionally smaller 

 than those of crayfishes which possess functional eyes, but they have in 

 the two cases characteristically different shapes. In crayfishes with 



