THE PATH OF DEGENERATION IN ANIMALS 185 



destroyed any functional activity in the lens and the 

 retina, but these parts none the less retain traces 

 of a complicated structure recalling their condition 

 when functional. 



In the Khynchocephala and Lizards examined 

 by W. B. Spencer, 1 there is to be found a series of 

 types representing the various stages of the 

 degeneration of the eye in the slow-worm. 



In the type Splienodon (Hatteria, fig. 62, A), the 

 organ in the adult is in the complete form. The 

 eye possesses a lens (c), a retina, (r), with com- 

 plicated histological structure. A nerve (n) places 

 the retina in communication with the brain. 



In Chamceleo (fig. 62, B), the degradation of the 

 organ has reached the following stage : the epi- 

 physis has a distal portion corresponding to the 

 eye, but the histological differentiation of this is 

 incomplete, neither the retina nor the lens being 

 distinct. Nervous fibres connect this with the 

 proximal portion which is hollow and in com- 

 munication with the brain. It thus represents 

 the second stage in the formation of the eye in 

 the slow-worm. 



In the types Lewder a and Calotes (fig. 62, c), the 

 chief degeneration is in the optic nerve, which has 

 partially disappeared, and no longer connects the 

 eye with the brain. The eye itself is not quite 



1 W. B. Spencer, On tJie presence and structure of the pineal 

 eye in Lacertilia (Quarterly Journal of Microscopical Science, 

 1886). 



