in water during variable time: only 1.5 min. in the lake trout and up
to 8-12 hours in sturgeons.

The method of artificial insemination most suitable for a given fish
species is determined by the properties of the gametes. Three methods
of roe insemination were being employed in pisciculture - dry, semi-
dry and wet, but at the present time the first of these has supplanted
the two others almost everywhere. This method is best for Salmonides
as fertilization in these fishes is accomplished in coelomic fluid. In
experiments performed on the lake trout roe (Fig. 2), the dry method
gave a high percentage of fertilization for all the milt dilutions tested,
and the semi-dry only if concentrated sperm suspensions were used;.

w hereas the use of the wet method always led to fertilization of a minor
number of the eggs only. However, when inseminating the sturgeon roe,
the best and most constant results were obtained with the semi-dry

m ethod (3), when roe and milt were collected dry, and the milt was
diluted just prior to insemination. The unfavorable action of the coelo-
mic fluid was thus avoided. .The dry method of insemination is less
suitable than the semi-dry and wet for those Teleostean fishes in which
spermatozoa are weakly activated or not at all activated in coelomic
fluid.

2. THE NUMBER OF MICROPYLES AND THE MECHANISM OF
THE BLOCK TO POLYSPERMY.

Both Salmonid and Acipenserid fishes are physiologically monospermic
animals, but the mechanism of protection against polyspermy presents
some differences in these groups. In Salmonides, as well as in other
Teleosts, the egg surface accessible for spermatozoa is reduced to a
single micropyle; that is, the diameter of its terminal canal hardly ex-
ceeds that of the spermatozoon head. Therefore, as long as the fertili-
zing spermatozoon remains in this canal, it mechanically blocks the way
to other spermatozoa. Later, as the fertilizing spermatozoon is engulfed
by the ooplasm, the discharge of the contents of the cortical alveoli
into the perivitelline space begins in the micropylar region, and the
secreted substance cause the agglutination of the approaching excessive
spermatozoa (4). Such a mechanism of block to polyspermy acts relia-
bly under any conditions of insemination. In experiments on the lake
trout all concentratiors of the sperm suspension used for artificial inse-
mination are invariably monospermic:.

The egg membranes of sturgeon eggs are supplied with several micro-
pyles (up to 13 in sevryuga, 33 in beluga and 52 in osetr). Usually,
only one spermatozoon penetrates the egg through one of the micropyles,
w hile the penetration of spermatozoa entering other micropyles is blocked
by the spreading of the cortical reaction. However, if the concentration
of spermatozoa around the egg is high, several spermatozoa can simultan-
eously penetrate the egg through different micropyles. Polyspermic ferti-
lization has as its consequence characteristic aberrant cleavage and

1038