508 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [18] 
and more noticeable according to the degree of its development. These 
motions, which cause the bursting of the shell which incloses the embryo, 
increase in violence till the moment when theyoung fish leaves the egg. 
Finally, there is formed in the shell of the egg a small opening which 
allows the young fish to slip out of his place of imprisonment. 
Hither the tail or the head generally appear first; sometimes the um- 
bilical bladder makes its appearance before either of the above-men- 
tioned members, But whatever part of the body emerges from the shell 
first, the young fish is not yet master of all its motions. 
It remains partly inclosed in its shell, and only gradually 
and by repeated efforts does it succeed in enlarging the 
opening of its prison; after a few hours it is entirely 
rige 23) free (Fig. 23), and can divest itself of a membrane which 
_ was only intended to protect it during the early stages of its develop- 
ment, and which was of no use whatever in forming any of the organs 
of the body. 
The space of time which elapses from the moment of fecundation till 
the fish is freed from its protecting cover is different with the different 
kinds of fish. With the pike, it is eight, ten, or fifteen days; with others, 
like the salmon, it is one or two months. 
The development of the fish progresses slower or quicker according to 
the temperature in which incubation takes place. Pike eggs placed in | 
water exposed to the rays of the sun, and which has not been renewed, 
are hatched after nine days, whilst other eggs which have remained in 
the shade in water which has been constantly renewed would require 
eighteen to twenty days for their entire development. 
CHAPTER IV. 
RAISING YOUNG FISH, AND THE CARE WHICH SHOULD BE BESTOWED 
ON THEM. 
§ 1.— Dissemination. 
During the first period after the fish has torn its protecting membrane, 
it is useless to give it any food, as the umbilical sack, which in certain 
fish, like the carp, is found in the abdominal cavity (whilst in others, 
like the trout and salmon, is outside this cavity and can be plainly seen) 
furnishes it with food until it is entirely absorbed. The time required 
for this differs in the different species of fish; thus the carp goes with- 
out food for two or three weeks. Salmon remain one or two months 
after being hatched in the incubating apparatus without taking any 
other food but that furnished by the umbilical sack, or perhaps by mi- 
croscopic animalcule found in the water. 
The necessity for other food asserts itself with the disappearance of 
this sack; and the further preservation and raising of yonng fish will 
have to follow one of the two methods described below, until further ex- 
perience has shown which of the two is positively to be preferred. 
