381 



a]icl 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 migJit form and even lay down the axis Of the embryo. 

 These, like the above, soon died. In all hybrid eggs, bnt particularly those 

 obtained from distantly related species, the period of gastrulation is one of 

 great mortality. The embryos usuallj' 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 esnbryos may in some cases remain alive for days, devel- 

 oping pigment, a rudimentary heart, pericardial cavity, etc. 



A very common deformity in the more 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 hybrids 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.^ 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, etc., promise well to carry their development to 

 completion. In every instance, however, regardless of how normal the 

 organogenetic 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- 



' A detailed description of these hybrids ai-e reviewed in a separate paper. 



