532 



H. H. Nevj?na?j 



made and afterward measured in order to see what proportion of 

 the yolk had been surrounded by the germ band. The results: 



H pures, 24.6 per cent of yolk covered; 

 H hybrids, 20.8 per cent of yolk covered; 

 M hybrids, 18.2 per cent of yolk covered; 

 M pures, 16.2 per cent of yolk covered. 



At 30 hours: An interesting condition between Stages 2 and 3 

 of Series i. Here the H pures had the blastopore almost closed 

 and the optic lobes well developed, resembling (/zj). The H 

 hybrids showed the germ band about three-fourths around the 

 yolk and the embryo in the primitive streak condition, slightly 

 more advanced than (Mj). M hybrids with germ band about 

 one-half around the yolk and a germinal shield better developed 

 than in M pures. Germ band in M pures less than one-half 

 around the yolk. 



The rest of the series offered only a few noteworthy differences 

 to the conditions seen in Series i. 



A tabulated account of these differences follows : 



a At 56 hours there was no marked difference in degree of 

 advancement between M pures and M hybrid, in both the con- 

 dition resembling closely {M4.). 



h At 70 hours, however, the M hybrids showed a marked 

 advantage over the M pures, the former resembling {m^) and the 

 latter {M^). 



c At the end of a week the M pures and M hybrids were deci- 

 dedly clearer within the egg membrane and admitted of camera 

 drawings. The drawings show the two strains to have been 

 practically identical in size, but the M hybrids were heavily pig- 

 mented both on body and yolk, while the M pures showed no pig- 

 ment on the body and only a few finely branched, grayish chro- 

 matophores on the yolk. 



d The H pures hatched as follows: 2 on eleventh day, 14 

 on twelth day, 2 on thirteenth day. The H hybrids hatched as 

 follows: I on eleventh day, 10 on fourteenth day, 4 on fifteenth 

 day, and i on sixteenth day. The remaining four showed decidedly 

 abnormal conditions like those shown in Figs. 3 to 8, and never 



