381 
and there die. In a few cases the vesicle was observed to be so large as to 
act as the yolk ball so that the protoplasm attempted to encompass it. 
Embryonic shield might form and even lay down the axis of the embryo. 
These, like the above, soon died. In all hybrid eggs, but particularly those 
obtained from distantly related species, the period of gastrulation is one of 
great mortality. The embryos usually enter upon the germ ring and shield 
stage rather normally and simultaneously, but from this period to the 
closure of the blastopore the greatest variation in stages obtains. In some 
of the less successful crosses most of the eggs never succeed in properly 
closing the blastopore, but come to a standstill so far as this process is con- 
cerned at various stages, and continue the rudimentary formation of an 
embryo in the embryonic shield. 
These aborted embryos may in some cases remain alive for days, devel- 
oping pigment, a rudimentary heart, pericardial cavity, etc. 
A very common defcrmity in the mcre successful embryos is the failure 
of the tail to bud out so that the embryos. very generally, are too short. <A 
striking instance of this fact appeared in the kybrids between Savelinus 
fontinalis, female, and Cristivomor namaycush, male. ‘This cross is quite 
successful, and the writer has succeeded in rearing 2,300 of them to finger- 
lings. Among this lot, a very large per cent. were deformed, and in every 
instance the deformity occurred in the region posterior to the anus. The 
portion anterior to the anus was normal in every way so far as proportions 
are concerned. The same is true of the caudal fin. But the region between 
this and the anus showed all degrees of shortening, the extremes appearing 
as if the caudal fin were directly set into the body of the fish. The anal fin 
was often wanting altogether, even in some that had the caudal peduncle 
otherwise normally developed.t. This process of the elongation of the caudal 
end of the embryo seems evidently a difficult one, giving rise to the common 
abnormalities in this region. In those crosses where a portion of the 
embryos succeed in laying down the fundamental organs such as the eyes. 
ears, brain, heart, muscles, ete., promise weil to carry their development to 
completion. In every instance, however, regardless of how normal the 
erganogenetic processes may at first be, they show a very clearly defined 
abortive influence in a short time. This begins to show itself shortly after 
the time when the circulation is established in the normal embryo. This 
fails to develop properly in all these hybrids that fail to complete their de- 
1A detailed description of these hybrids are reviewed in a separate paper. 
