Heredity in Fuudidus Hybrids 145 



time and tend to adhere in a very unpleasant way to the instru- 

 ments used for handhng them. For these reasons, the eggs of 

 F. heterocHtus are deemed unfit for experiments of the present 

 sort and attention has been given solely to the eggs of F. majahs. 



The species F. majalis develops only about two-thirds as rapidly 

 as the species F. heretoclitus, the former reaching the hatching 

 period in about three weeks; the latter in about two weeks. The 

 same general time ratio prevails throughout the entire develop- 

 mental process. In F. majalis the second cleavage occurs in about 

 four hours after fertilization, while in F. heteroclitus it occurs in 

 about three hours. Hybrid eggs (F. majalis 9 F. heteroclitus c?) 

 show a slight acceleration of early cleavage as compared with 

 pure-bred F. majalis eggs. 



Expecting the influence of the foreign spermatozoon to be 

 very slight at so early a period as the second cleavage, a very large 

 number of eggs were used and as many experiments were per- 

 formed as the time would permit. 



In all experiments it was found necessary to distinguish several 

 stages between the 2- and the 4-cell conditions. As a rule the 

 following stages could be distinguished: 



a. Complete 4-cell, shamrock-shaped, with each blastomere 

 separated from its neighbors by a deep notch (Fig. 7). 



b. Incomplete 4-cell, with the notches of the second cleavage 

 less deep than those of the first (Fig. 6). 



c. 3-cell, in which the second cleavage had occurred in one 

 of the blastomeres and not in the other. 



d. 2-cell with second cleavage furrow just beginning (Fig. 5). 



e. Complete 2-cell, with the blastomeres separated by deep 

 notches (Fig. 4). 



/. Incomplete 2-cell, with the first cleavage just beginning 

 or incomplete (Figs, i, 2 and 3). 



For the sake of brevity these stages are designated as follows: 

 4-cell, 4-minus, 3-cell, 2-plus, 2-cell, 2-minus; the 4-minus being 

 valued at 3^, 2-plus at 2\, the 2-minus at i|, and the rest at face 

 value. 



Eggs that show no signs of cleavage are designated as "un- 

 cleaved." The majority of the latter have either failed bv chance 



