388 CHARLES H. SPURGEON. 



the cornea in other Crustaceans; so that the eye may be unfitted 

 for distinguishing form, the creature may yet possess the faculty 

 of perceiving the small amount of actinic rays of light which 

 might penetrate into its subterranean abode . . . ; the cornea 

 also exhibits an appearance of being divided into a few imperfect 

 corneals (facets) at the apex of the organ, and the structures 

 behind these into chambers, to which a small but distinct optic 

 nerve is given." He also noted that the eyes are not pigmented. 



I find that the eyes of C. pellucidus from Indiana caves and of 

 C. setosus from Missouri caves show neither "corneals" (facets) 

 nor "chambers, to which a small but distinct optic nerve is 

 given." 



The next writer on the eyes of blind crayfish was Leydig (1883). 

 He stated that the cornea in C. pellucidus is lamellated, without 

 pigment and without facets. His description of the internal 

 structures of the eye is very general and indefinite. 



Packard (1888) in his memoir on "The Cave Fauna of North 

 America" describes and illustrates the form and structure of the 

 eyes of C. pellucidus from Indiana and Kentucky caves and C. 

 hamulatus Cope and Packard from Nickajack cave, Tennessee. 

 He found that in both species the cornea is without facets and 

 that the hypodermis is of the same thickness in the retinal region 

 as in other parts of the eye; also that the optic nerve and optic 

 ganglion are present. 



The following year (1889) Garman published Faxon's descrip- 

 tion of C. setosus to which reference was made in the opening 

 paragraph. 



Parker (1890) published a paper on "The Eyes in Blind Cray- 

 fishes." He had access to C. hamulatus and C. setosus. The 

 major part of his paper deals with C. setosus. He emphasizes the 

 uniform thickness of the cuticula, the nearly uniform thickness 

 of the hypodermis and the relation of the size and conical shape 

 of the optic stalk to the amount of degeneration, as well as the 

 histological structure of the degenerated eye. He also called 

 attention to the relation of the axis of the cone, which is the 

 terminal part of the optic stalk, to the axis of the stalk itself. 



The most striking characteristics of the gross anatomy of the 

 eyes of C. setosus and C. pellucidus are smallness, lack of pigmen- 



