EYES OF CAMBARUS SETOSUS AND CAMBARUS PELLUCIDUS. 39 1 



The part of the degenerated eye of the blind crayfish which is 

 of chief interest is the retinal hypodermis. Here the largest 

 amount of degeneration has taken place. The optic ganglion, 

 optic tract and brain show little or no signs of degeneration. 

 The condition of these structures is well illustrated by photo- 



FiG. 7. A secondary thickening of the hypodermis from the antero-median 

 part of an eye of C setosus. 



micrographs B, C and D. The optic nerves (Fig. 8 and photo- 

 micrographs C and E) connecting the retinular cells with the 

 optic ganglion are also present but they are not as well developed 

 as the above mentioned structures. 



It is probable that when the embryology of the eye of the 

 blind crayfish is worked out, we may be able to definitely identify 

 the retinal cells shown in Fig. 8. The eyes of a C. setosus 15 mm. 

 long show about the same amount of degeneration as the eyes of 

 adults. The arrangement and general appearance of the retinal 

 cells of the hypodermis, shown in Fig. 8, is comparable to an 

 early embryonic condition found in the developing eyes of 

 many Crustacea, the bee and other Arthropoda. 



Parker states that the hypodermis in C. setosus is "very nearly 

 uniform in thickness." I find that the retinal hypodermis in C. 

 setosus and C. pellucidus is quite irregular as to thickness. Some- 

 times there are as many as three and four different thickened 

 regions in a single section. These thickened places in the 

 hypodermis are found at various places around the anterior end 

 and the sides of the optic stalk. The principal and most common 

 thickening is in the anterio-lateral part of the optic stalk, as is 

 shown in Fig. 5 and photomicrographs B, C and E. Secondary 

 thickenings are sometimes low on the sides of the optic stalk, as 

 illustrated by Fig. 6 and photomicrograph A. Fig. 7 represents 

 a type of the secondary thickenings. It was taken from a portion 

 of the hypodermis along the anterio-median part of the right 

 eye of C. setosus. The most highly developed or the least 



