194 REPOET OF COMMISSIONER OF FISH AND FISHERIES. 



Fig. 5 shows the egg 4 days old. Central area clearer than at 3 

 days. 



Fig. 6 represents le egg at 5 days old, or an age of 125 t. n., and 

 shows now for the i st time the presence of a secondary ring, not 

 quite complete, with vesicles on both sides of it. The inner ring is of 

 about the same appearance as on the day previous. This secondary 

 *'ring" is the eoiter edge of the germ disk or blastoderm and forms 

 the margin of the blastopore. 



Fig. 7 shows the egg with 6 full days' growth at 57° F., or 150 t. u. 

 The blastoderm is now well developed and has grown sufficiently to 

 pass the zone of vesicles. It is a very interesting as well as very 

 delicate stage of the egg. Phenomena appear that are not seen the 

 day previous nor the day following. It is at this time that the laying 

 of the " neural keel" or forming of the body outline of the fish takes 

 place. This outline can be quite readily detected the following day 

 at the same water- temperature. 



Fig. 8 represents the growth of the germinal layer halfway down 

 the egg. Its edge, previously referred to as forming the "ring" or 

 "loop" or blastopore, has the appearance of an addled ring. The 

 body outline of the fish is now seen for the first time, the tail extend- 

 ing down to the edge of the ring. The relative positions of the tail 

 of the fish and the ring do not change. The edge of the germ disk, in 

 its further growth finally encircling the egg, seems to remain attached 

 at this point and closes up in the shape of a continuously diminishing 

 loop, disappearing after the tenth day at 57° F. 



Fig. 9, at 200 t. u., shows a partial closing of the loop and a faint 

 differentiation of the head into two eye-spots; also the appearance of 

 a line crossing the body back of the head, which in a few days seems 

 to defiect from this position and extend out forward. This line finally 

 branches out and assumes the bright color of an artery. 



Fig. 10, at Si days old, or an age of 215 t. u., shows the loop dis- 

 tinctly as such. Body outline clearer. 



Fig. 11 shows the egg on the tenth day, or 9 full days old, 225 t. u. 

 The loop is closed, and its remains may be seen hanging to the tail of 

 the fish. The artery may now be seen extending out from the head, 

 although it has not yet assumed its bright-red color. The fish is now 

 practically formed, though the germ layer is still quite tender and 

 liable to rupture. 



One of the commonest monstrosities among young salmon is that of 

 tailless fish; and ks this thickened blastodermic ring forms the caudal 

 plate, it is thought that an injury to the embryo caused by rough 

 treatment at this time may be responsible for the loss. 



Fig. 12 shows the egg at 14 days old, or 350 t. u. The artery pro- 

 jecting out from the head has assumed color, the tail is bent upward, . 

 and the fish is capable of motion. It is now well out of the tender 

 stage, and must be kept free and clean to insure that degree of aera- 

 tion which the increasing color of the artery shows that it requires. 



