EYES OF CAMBARUS SETOSUS AND CAMBARUS PELLUCIDUS. 389 



tation and inconspicuousness. These features are shown in 

 Figs. I and 2. 



The eyes of all the blind crayfish examined are nearly covered 

 by the rostrum, from a dorsal view, while the eyes of normal 

 crayfish are only slightly concealed by the rostrum. However 

 the eyes of the young blind crayfish are relatively larger than 

 they are in the adult. The relative size of the eyes of C. setosus 

 and C. propinquus (?) is shown in Figs. 2 and 3. 



Size and pigmentation make the eyes of normal crayfish con- 

 spicuous. The eyes of blind crayfish are smaller and without 



mvis. 



5 



Fig. 4. Outline of the eyes of C. pellucidiis 10 mm. long. 



Fig. 5. Horizontal (longitudinal) section of the eye of C. setosus, with the cuti- 

 cula removed. 



pigment. The relative shortness of the optic stalk in the eyes of 

 blind crayfish tends to make them inconspicuous. 



The distal end of the optic stalk of the eyes of the blind cray- 

 fish examined is roundish or almost hemispherical in shape. 

 Fig. 4 which shows this was made with the aid of a camera 

 lucida, from a fresh specimen of C. pellucidus, 10 mm. long. The 

 same general form of the eye is shown in photomicrographs A and 



B, which were made from a horizontal section of the eyes of C. 

 setosus. In no case out of fifteen series of sections of the eyes of 



C. setosus and C. pellucidus have I found the exaggerated conical 

 form figured by Packard and by Parker. Crayfish killed in 

 Perenyi's fluid and kept in 85 per cent, alcohol for a few weeks 



