126 



BLIND VERTEBRATES AND THEIR EYES. 



brane is represented by blood corpuscles and by a few cells with elongated nuclei 

 whose longer diameters are parallel with the optic nerve. 



Measurements of the Eyes of Typhlichthys subterraneus. 



TROGLICHTHYS ROS^E. 



In December, 1S89, Garman published an account of cave animals collected 

 by Miss Ruth Hoppin in Jasper County, Missouri. Among them were a num- 

 ber of what were supposed to be Typhlichthys subterraneus Girard. A compari- 

 son of the eyes of two of the specimens collected by Miss Hoppin with the eyes of 

 specimens of Typhlichthys subterraneus from Mammoth Cave showed that the 

 western specimens represented a distinct species, and that Kohl must have based 

 his account of the eye of Typhlichthys on specimens from Missouri. 



In the spring of 1897, I visited the caves examined by Miss Hoppin, at Sarcoxie, 

 Missouri, but as my stay was limited and the caves were full of water I did not 

 succeed in getting any additional material. In September, 1898, through a grant 

 from the Elizabeth Thompson Science Fund I was enabled to make another and 

 this time successful effort to secure this highly interesting material. 



Kohl described the eyes of Typhlichthys, basing his account on two specimens 

 respectively 36 and 38 mm. long. Dr. Mark informed me that at least one of 

 these specimens came from Missouri, and Kohl's account was certainly drawn 

 from Missouri specimens only. 



He found that the bulbus is nearly spherical, with a diameter of 0.04 mm. 

 The orbit is a very flat cavity that offers little protection to the eye. Suborbitals 

 are totally wanting and in their place is a cartilaginous protecting capsule, placed 

 over the bulbus dorsally and laterally, and made up of several cartilaginous plates 

 0.02 mm. thick. Between the plates the connective tissue frequently contains 

 thick and large nuclei which are sometimes united into groups. One such mass 

 he thinks has been taken for the lens by Wyman (Putnam, fig. 5). It lies 0.195 

 mm. from the outer surface of the epidermis. All tissues covering the eye show 

 absolutely no difference from neighboring parts. Eye muscles are not found, but 

 sometimes there are stiff connective tissue strands connecting the cartilaginous 

 bands with the tissues immediately surrounding the eye. The eye in the speci- 

 mens examined he considers in the stage of the formation of the secondary eye 

 vesicle. There is still a large cavity present representing the primitive eye cavity 

 which is only being encroached upon by the invaginating outer cells, which in 

 part are precociously ganglionic, sending each a process to the optic stalk. The 

 optic stalk no longer shows a cavity, which he assumes became obliterated by the 

 direct ingrowth of nerve fibrils and not in the usual way. The invagination of 



