540 



H. H. N 



etuman 



There were probably many unripe and stale eggs in this lot, as 

 no care was takento select the best males or females. 



5 A large number of eggs from a good H female were divided 

 into two lots, fertilized with both species of sperm, and after they 

 had reached a stage where there seemed to be about equal num- 

 bers of 1 6 and 32-cell stages the two lots were killed and examined, 

 with the following results: H pure, 38 thirty-two-cell stages, 

 44 sixteen-cell stages, and 29 uncleaved. H hybrid, 33 thirty- 

 two-cell stages, 31 sixteen-cell stages, and 42 uncleaved. Of eggs 

 cleaved H pure showed 46.3 per cent in 32-cell stage and H hybrid 

 44.6 per cent. The difference was so slight that it was not sig- 

 ficant. Four other experiments similarly conducted gave results 

 approximately like those just detailed. In some the percentages 

 lightly favored the pure strain and in others the hybrid strain. 

 The conclusion was reached that there was no measurable differ- 

 ence in time rate of cleavage up to the 32-cell stage, at least. 



6 Several experiments were conducted like those just described 

 except that the eggs were allow^ed to develop until the blastodiscs 

 had begun to spread out over the yolk. They were then killed 

 and examined before any shrinkage had taken place. 



a This lot allowed to develop for sixteen hours, and twenty-five 

 eggs, selected at random, were transferred to another vessel, where 

 the blastodisc diameters were measured with ocular micrometer. 

 Results: H pure average 20.4 mm.; H hybrid 16.6 mm. 



b Allowed to develop 14 hours: Average diameter of twenty 

 H pures was 16.8 mm., that of /^ hybrids 15.4 mm. 



c After 20 hours : Average diameter of twenty H pures was 

 22.6 mm., that oi H hybrids 20.1 mm. 



d After 20 hours: H pures 21.3 mm., H hybrids 20.8 mm. 



7 This series only F. heteroclitus strains: After 24 hours the 

 two strains were killed and examined. It was found that the H 

 pures were on the average in the condition of {?n^), while H hybrids 

 were in that of (Mj)". The difference was very marked. 



2 Later Stages 



A few detailed camera drawings of whole mounts of later stages 

 were made and a plate of these figures will show better than a 



