THIRTEENTH ANNUAL MEETING. 195 
ON THE FORCES WHICH DETERMINE THE 
SURVIVAL OF FISH EMBRYOS. 
BY JOHN A. RYDER. 
Mr. PresipentT: Unfortunately the programme announces the 
title of my communication in a form somewhat different from 
the one actually chosen for my paper, although in reality there 
is no great difference between the two. I propose to-day to 
discuss some of the causes which limit the survival of fish em- 
bryos. It is well known to fish-culturists and naturalists that 
there is a great amount of variation in the number of ova pro- 
duced by different species of fishes. This great variation is sig- 
nificant and can be accounted for on no other ground than this: 
that it must be supposed that there is a great over-production of 
eggs in order to make up for the losses in the struggle for exist- 
ence, as indicated in the first place by Malthus and afterwards 
elaborately worked out by Mr. Darwin. This disparity in the 
number of germs produced by different species is so great as to 
astound us at first. There are species, for instance, in which the 
number of germs produced by the female fish would not exceed 
twenty. There are some, indeed, that only produce five or six. 
Again, there are species which produce as many as 10,000,000, 
Now, how is this difference to be explained? It isa singular 
fact that the greatest number of eggs appear to be produced by 
those fishes that take the least care of their progeny, viz., those 
species which discharge their eggs into the open sea and com- 
mit them to the mercy of the winds and waves, such as the cod- 
fish and flounders and many of the Clupeoids. Whereas the re- 
verse seems to be true, in the case of those fish which studiously 
take care of their eggs, or incubate them inside of their ovaries 
—as for instance the Hmdiotocoid fishes of the west coast—or as 
in another case (Gameusta) within the ovarian follicle, modified 
into a quasi-placental structure; or, as in the case of the catfish, 
where the male hovers over the adherent mass of ova and forces 
the water through them, or yet again where the eggs are retained 
in a pouch underneath the abdomen, as in the pipe-fishes, or are 
