TJie Process of Heredity C25 



and bloodless, mere strands that continued to contract rhythm- 

 ically within an enormous empty pericardium. A number of 

 these abnormal conditions will be described and discussed in 

 a later section of this paper. The hybrids, although a hetero- 

 geneous lot, still showed about 60 per cent of normal, healthy 

 specimens. 



The M hybrids were too obscure within the envelope to admit 

 of accurate camera drawings. A typical specimen, however, 

 was dissected out of the envelope and, after being quieted with 

 chloretone, was drawn (Plate IV, mg). The general body form 

 is similar, except that it is larger, to that of the average H pure 

 of 114 hours {H8). The caudal fin was well developed and the 

 eye had assumed a form almost definitive. Heavy blackish pig- 

 ment, in the form of large chromatophores, had darkened the sur- 

 face of the yolk sac, while slender grayish, much branched chro- 

 matophores were distributed over the surface of the body. 



The M pures (Plate IV, Mg) were on the average about the same 

 in size as the M hybrids. There was a small amount of blackish 

 pigment on the yolk, but none at all on the body. 



The verbal description of the stages figured in the table ends 

 here. The further description of the series will be carried on with- 

 out numbering the stages. The sections, instead of being num- 

 bered by stages will be headed with the number of days that have 

 elapsed since fertilization. 



At 10 days: The general size of the H pure and H hybrid 

 embryos was about the same, the chief difference between the 

 two strains being that the healthy H hybrids were a little 

 more heavily pigmented than the average H pures. A few 

 H hybrids were especially dark. The M hybrids showed a heavy 

 pigmentation on the top of the head and down the middle of the 

 back. The vitelline vessels were also very heavily pigmented, 

 about like that of the average H pure at 96 hours {Hy). The 

 general size of the M hybrids was less than that of the M pures. 

 There had appeared a change within the last two days in the M 

 hybrids. They seemed to have lagged behind the M pures after 

 having been at first ahead of the latter and, for some time past, 

 practically on an equality with them. The M pures although 



