54 BLIND VERTEBRATES AND THEIR EYES. 



TYPHLOPS LUMBRICALIS. 1 



Typhlops linnbricalis (Linnaeus), a blind snake, is generally distributed in the 

 West Indies and Guiana. The specimens examined were obtained in the neigh- 

 borhood of Cafias, Province Pinar del Rio, Cuba. It is a burrowing form that 

 lives just beneath the surface, being thrown out even by the plow. 



The snakes were first placed in formalin and after a few days were transferred 

 to alcohol. Only one young specimen was obtained, and it was preserved in 

 Zenker's fluid. For decalcification, the heads of some were placed for at least 3 

 days in 10 per cent nitric acid and others in Perenyi's fluid from i to 2 weeks. One 

 series was stained by the iron haematoxylin process, the others with haemalum and 

 eosin. It was very difficult to obtain satisfactory sections and especially complete 

 series from the specimens, since no method was found to decalcify properly and to 

 get the integument in condition for sectioning. 



The lengths of the individuals examined were 10, 20, 21, and 21.5 cm. The 

 color is brown above, on the ventral side it is yellowish white. The body is cov- 

 ered with scales of uniform size, while those of the head are somewhat larger. The 

 surface of the entire body is very smooth and shining and rather hard. The tail, 

 which is about one-twentieth of the body's length, ends in a short, sharp spine. 

 The mouth is small and lies on the ventral side some distance back from the tip of 

 the snout. 



GENERAL ACCOUNT OF EYES IN SNAKE. 



Snakes differ from other animals in having the edges of the two eyelids entirely 

 grown together. A disk-shaped, conjunctival sac is thus formed and the layers 

 over the eye between this sac and the exterior form the "brille." Six weakly 

 developed muscles are present. The 4 straight ones arise in the neighborhood of 

 the foramen opticus, while the 2 oblique ones arise from the surface of the prefrontal 

 which is turned toward the eye socket. 



Closely connected with the eye is Harder's gland, whose function is doubtful. 

 Leading from this gland is a single duct, which either empties into the duct from 

 Jacobson's gland or directly into the mouth cavity. The secretions of the gland 

 are thus not functional in connection with the eye. 



The sclera consists of closely woven fibers. Ciliary muscles are not found, but 

 in -\t In the iris is a great bundle of equatorial muscle fibers running obliquely, 

 .vliich seem to be a continuation of the iris musculature. The ciliary processes are 

 weakly developed. 



The retina consists of the usual layers. The nerve-fiber layer is very thin (0.003 

 to 0.004 nim.). 



The ganglion-cell layer consists of a single, rarely two, layer of small cells, each 

 with a very large- nucleus (0.012 to 0.013 mm.). The inner reticular layer contains, 

 al apparently regular intervals, elongated, oval nuclei (0.042 to 0.045 mm.). The 

 inner nuclear layer consists of two kinds of cells (0.052 to 0.054 mm.). The outer 

 relicular layer is very thin (0.004 to 0.005 rnm.). 



1 By Effa Funk Muhsc. Si-c Hint. Bull. vi. p. 261, 1903. 



