Fig. 163.—Sleek Sculpin, Psychrolutes paradoxus (Günther). Puget Sound.
"(a) The first extends from the appearance of the eye till the embryo is 4-5 mm. long. This period is characterized by a normal palingenic development, except that the cell division is retarded and there is very little growth.
Fig. 164.—Agonoid-fish, Pallasina barbata (Steindachner). Port Mulgrave, Alaska.
"(b) The second period extends till the fish is 10 mm. long. It is characterized by the direct development of the eye from the normal embryonic stage reached in the first period to the highest stage reached by the Amblyopsis eye.
Fig. 165.—Blindfish of the Mammoth Cave, Amblyopsis spelæus (De Kay). Mammoth Cave, Kentucky.
"(c) The third, from 10 mm. to about 80 or 100 mm. It is characterized by a number of changes which are positive as contrasted with degenerative. There are also distinct degenerative processes taking place during this period.
"(d) The fourth, 80-100 mm. to death. It is characterized by degenerative processes only.