"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 character.
"The lens is first to show degenerative steps and disappears entirely before the fish is 10 mm. long.
Fig. 166.—Blind Brotula, Lucifuga subterranea (Poey), showing viviparous habit. Joignan Cave, Pinar del Rio, Cuba. Photographed by Dr. Eigenmann.
"The optic nerve appears shortly before the fish reaches 5 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 rosæ.