Parker. — Blind Crayfishes. 



EXPLANATION OF FIGURES. 



ABBREVIATIONS. 



con. cone. mb. basement membrane. 



ct. cuticula. nl. con. nucleus of cone-cell. 



gn. opt. optic ganglion. nl. hd. nucleus of hypodermis. 



hd. hypodermis. n. opt. optic nerve. 



r. retina. 



The specimens from which the following figures were taken were killed and 

 preserved in strong alcohol, and stained in Czocher's alum-cochineal. The cray- 

 fish from the optic stalk of which Figure 1 was drawn was 6 cm. long. That from 

 which the remaining figures were made was 4.4 cm. long. 



Fig. 1. A longitudinal horizontal section through the right optic stalk of Cam- 

 barus' setosus, Faxon. The histological detail is given in the hy- 

 podermis only. The optic ganglion and the optic nerve are tinted. 

 Between these structures and the hypodermis the space is filled with 

 a loose connective tissue. X 65. 



" 2. A longitudinal horizontal section through the right optic stalk of Cam- 

 barus pellucidus, Tellk. This drawing was made in the same manner 

 as Figure 1. X 65. 



" 3. An enlarged drawing from the distal end of the section which immediately 

 follows that from which Figure 2 is taken. This figure shows the details 

 in the retinal enlargement of the hypodermis. The space between 

 this enlargement and the cuticula was artificially produced, x 275. 



" 4. Tangential section of the hypodermis from the side of an optic stalk of 

 Cambarus pellucidus. X 275. 



" 5. Tangential section of the superficial portion of the retinal thickening in 

 the eye of Cambarus pellucidus. X 275. 



" 6. Tangential section of the deep portion in the retinal thickening of the eye 

 of Cambarus pellucidus. This section is taken from the same series 

 as the one from which Figure 5 was drawn. X 275. 







