EYES OF CAMBARUS SETOSUS AND CAMBARUS PELLUCIDUS. 393 



rhabdom are absent in the eyes of C. setosus and C. pellucidus. 

 Some of the sensory cells are present even though they may be 

 no longer functional. I believe we may feel reasonably sure of 

 the identity of some of the cells found in these degenerated eyes. 



in Fig. 8 there are at least three kinds of cells 

 shown; (i) the large, oval, dark staining, granu- 

 lar cells with several nuclei, the "granular bod- 

 ies," "degenerated representatives of the cones 

 in the normal e3^es" of Parker, (2) elongated cells 

 or nuclei with fibers, and (3) small, round, gran- 

 ular cells with clear nuclei. 



The large, oval, dark staining, granular cells 

 with several nuclei are probably pigment cells 

 as they are the only similar cells found on both 

 sides of the basement membrane in the func- 

 tional eyes as well as in these degenerated ones. 

 Parker found "granular bodies" on the distal 

 side only of the basement membrane and called 

 them "degenerated representatives of the cones 

 in the normal eye." 



The elongated cells with fibers compare with 

 the retinulae of the functional eye. The retin- 

 ulse are the only cells with fibers in retina. 



The small, round, granular cells with clear 

 nuclei may be degenerated cone cells or the 

 "undifferentiated hypodermal cells" of Parker. 

 But most of these cells are too far removed from 

 the cuticula to be " undifferentiated hypodermal cells ' ' which have 

 secreted the cuticula. The cuticula is thin in the retinal region. 

 According to Watase, the sensory cells of the ommatidium secrete 

 the cuticula. I am inclined to believe that the small, round, 

 granular cells are degenerated cone cells. 



Comparing the sections of the eyes of C. setosus and of C. 

 pellucidus it is found that the eyes of setosus are little if any 

 more degenerated than those of pellucidus. Irregularities are 

 common in the retinal hypodermis of the eyes of these crayfish. 



Whether the eyes of the blind crayfish have passed through a 

 higher stage of development and then degenerated or whether 



Fig. 9. The om- 

 matidium of Cam- 

 bants. (After Wa- 

 tase.) 



