The Process of Heredity 533 



hatched. The first 11 H hybrids to hatch looked darker and 

 larger than the hatched H pures. The M pures hatched as fol- 

 lows: 4 on twentieth day, 6 on twenty-first day, 4 on twenty-sec- 

 ond day; the rest died. None of the M hybrids hatched. Eigh- 

 teen out of twenty of them were living on the twenty-fifth day and 

 micrometer measurements of head diameters were made for the 

 sake of comparison with those of the other strain on hatching. 

 The following were the measurements 1.28, 1.24, 1.24, 1.14, 1.45, 

 1.24, 1. 16, 1.36, 1. 14, I.I, .61, 1.28, 1.4, 1.36, 1. 12, .82, .97, 1.24. 

 Average 1.06+ mm. Average head diameters of M pures on 

 hatching was 2 mm.; that of jF/ pures, 1.24 mm. Except for the 

 presence of three dwarfed specimens the average of the M hybrids 

 would have been a little greater than that of the H pures and the 

 specimen with head diameter of 1.45 mm. was larger than any of 

 the H pures. Even this large specimen, however, was not as 

 large as the smallest of the M pures measured. 



Series 5, July 5, igo6. In this series no micrometer measure- 

 ments were made, but as only ten embryos were followed for each 

 strain, it was possible to become personally acquainted with nearly 

 all of the specimens and judgment was based on this acquaintance. 



At 25 hours: H pure, germ band one-half around yolk. H 

 hybrid germ band one-third around yolk. No difference between 

 majalis strains. 



At 48 hours: H pure, between (i^j) and {H^). Average 



somites, 8. 

 H hybrid, slightly less advanced than (Hj). No somites. 

 M hybrid slightly more advanced than (m/f). 

 M pure, slightly more advanced than {M4). 



At 62 hours: No very marked difference between H pures and 

 H hybrids. M pures and hybrids also almost on an equahty. At 

 this time there seemed to be a halting on the part of the two strains 

 that had been ahead, giving an opportunity for those that had 

 been distinctly behind, temporarily to overtake them. 



At 68 hours : Six out of ten H pures had slow and feeble heart- 

 beats. No heart-beats in any of the other strains. 



At 76 hours: In size and general body form the H pures were 



