THIRTEENTH ANNUAL MEETING. 197 
back, where the young fish seem to undergo a sudden change of 
coloration, rendering them much more difficult of detection in 
the water. A certain writer, speaking of sticklebacks, asserts 
that the male will acutally catch and return the young fish to the 
nest during the first day or two after hatching. This change of 
coloration may possibly be dependent upon the action of light. 
Regarding the survival of fish embyos, the specific gravity of the 
eggs of different species, is another point to be considered. Thus, 
the eggs of the cod, mackerel and crab-eater, are buoyant and 
tend to come to the surface of the water. Others as persistently 
sink. In other fish ova the oil drops are so arranged as to per- 
sistently turn the germinal disc to the top, as is the case with 
the salmonoids; this relation is reversed in the case of floating 
eggs, in which the vitellus is on the top and the germinal disc 
underneath. 
Judging from the attempts made to rear and multiply certain 
feral mammalia, we know that confinement tends to produce 
sterility. I believe that under such conditions certain changes 
are effected in the ovaries of fishes in their efforts to free them- 
selves from the bondage imposed by man, and that the physio- 
logical organization of the eggs is destroyed. 
The distribution of food—especially articulate food—is also 
an element to be considered with respect to the survival of young 
embryos. In various regions of the globe certain living aquatic 
food seems to swarm at particular times and in fixed localities. 
I know this to be so from my own observations in the vicinity of 
Philadelphia, and especially in the swamps and low grounds of 
New Jersey. It is impossible to predicate from outward appear- 
ances what particular forms of articulates will be encountered 
until you are on the ground and make a careful examination, 
and there is no doubt in my mind that the absence from streams 
of certain small forms of articulates, such as Daphnids and Cofe- 
poda, have a great deal to do with the survival of the young fish. 
As this kind of food is absent or abundantly present, so will the 
young fishes perish or survive. 
There is another cause to which may be attributed the destruc- 
tion of the fish embryos, and that may be embraced under the 
head of “shocks” which pervert development. We know, for 
