222 



Adaptations of Fishes 



trasted with degenerative. There are also distinct degenera- 

 tive processes taking place during this period. 



" (d) The fourth, 80-100 mm. to death. It is characterized 

 by degenerative processes only. 



"The eye of Amblyopsis appears at the same stage of growth 

 as in normal fishes developing normal eyes. The eye grows but 

 little after its appearance. 



"All the developmental processes are retarded and some of 

 them give out prematurely. The most important, if the last, is 

 the cell division and the accompanying growth that provide 

 material for the eye. 



." The lens appears at the normal time and in the normal way, 

 but its cells never divide and never lose their embryonic char- 

 acter. 



"The lens is first to show degenerative steps and disappears 

 entirely before the fish is 10 mm. long. 



"The optic nerve appears shortly before the fish reaches 5 



FIG. 166. Blind Brotula, Lucijuga subterranea (Poey), showing viviparous habit. 

 Joignan Cave, Pinar del Rio, Cuba. Photographed by Dr. Eigenmann. 



mm. It does not increase in size with the growth of the fish 

 and disappears in old age. 



"The scleral cartilages appear when the fish is 10 mm. long; 

 they grow very slowly, possibly till old age. 



"There is no constant ratio between the extent and degree 

 of ontogenic and phylogenic degeneration. 



"The eye is approaching the vanishing point through the 

 route indicated by the eye of Troglichthys rosa. 



"There being no causes operative or inhibit! ve, either within 

 the fish or in the environment, that are not also operative or 



