The Process of Heredity 539 



Series H, June 23, igo"/. H pures hatched chiefly on the 

 twelfth and thirteenth days. H hybrids hatched as follows: 10 

 per cent on the thirteenth day, 25 per cent on the fifteenth day, 

 30 per cent on the sixteenth day. The remaining 35 per cent did 

 not hatch. M pures hatched some time after the eighteenth day. 

 About thirty were seen swimming in the dish on the twenty-first 

 day. 



Data Derived from the Examination of Preserved Material 



Various series were watched and when some doubtful or espec- 

 ially interesting stage was reached a sufficient number of embryos 

 were killed in picro-acetic, and examined afterwards at leisure. 

 Additional and confirmatory data on several points was obtained 

 in this way. 



I Rates of Cleavage 



1 The eggs of a large F. majalis female were divided into two 

 lots of approximately equal size and fertilized simultaneously 

 with the milt of the two species. After three hours development 

 eggs were killed and examined with the following results : M pure 

 showed 158 four-cell stages, 2 three-cell stages, 3 two-cell stages, 

 and four uncleaved. M hybrid showed: 89 four-cell stages, 2 

 three-cell stages, i two-cell stage, and 114 uncleaved. 



2 Another lot of majalis eggs treated in the same way. M 

 pure 51 four-cell stages, 4 three-cell stages, 3 two-cell stages, and 

 38 uncleaved. M hybrid, 32 four-cell stages, 2 three-cell stages, 

 I two-cell stage and 54 uncleaved. 



3 Eggs of one heteroclitus female used, fertilized with both 

 species of sperm. After three hours there were: H pures, 41 

 four-cell stages, 5 two-cell stages, 54 unsegmented; H hybrid, 13 

 four-cell stages, 3 two-cell stages, 80 unsegmented. 



4 Same as 3, but a large lot of mixed eggs from over a dozen 

 females were used. These were divided, after stirring thoroughly 

 into two lots and fertilized with two species of sperm. At the 

 end of three hours they were killed in picro-acetic acid, and 

 examined. Results: H pure, 308 four-cell stages, 63 two-cell 

 stages, 563 uncleaved. H hybrid, 214 four-cell stages, 18 two- 

 cell stages, 742 uncleaved. 



