363 
Practically all of the eggs were normally impregnated, a very few of 
the eggs fell directly into four and six cells. ‘The rate of development was 
the same as the normals, until the later stages, when the hybrids fell 
behind, as shown in Table 8. The table would indicate that the hybrids 
were a little slower in their cleavage, but this is so slight that no value 
can be placed on it, considering the difficulty in telling exactly the moment 
when a new set of furrows begin. 
Many of the eggs go far enough to form the embryonic ring and the 
embryonic shield. The protoplasm continues to spread over the yolk until 
it is encompassed about two-thirds the way, or nearly closed. The embryo, 
however, does not form in the shield as it should. I have seen many eggs 
forming the germ ring and embryonic shieid perfectly. The protoplasm 
continues to grow over the yolk. but the embryo fails to develop perfectly. 
It is usually much too short and often with the blastopore about closed, 
there has failed to develop any embryo at all in the shield, the latter re- 
maining a mere mass of cells. 
TABLE 3. 
ie | FUNDULUS FUuNDULUS 
| x x 
FUNDULUS. | TAUTOGLABRUB. 
| 
Fertilization. 9.30 A. M., July 4, 9.30 a. M., July 4. 
Begin. 2 cells. iit aley i leary 
Compl. 2 cells. 11.35 11,35 
Begin. 4 cells. 11.50 11.46 
Comp. 4 cells. | 12.20 12.10 
Begin. 8 cells. 12.25 12-15 
Compl. 8 cells. 12.45 12.40 
Begin. 16 cells. 12.50 12.45 
Late segment 12.30 P. M., July 5. 12.30 Pp. M., July 5. 
Vs over yoke. 12.00 m. July 6. 12.00 M., July 6. 
Blast. closed. 12.00 m. July 7. | Had stopped in previous stage. 
No embryo differentiated. 
Tautogolabrus adspersus, female. 
x 
Fundulus heteroclitus, male. 
This cross was attempted but once and the development followed to the 
16-cell stage. Sixteen per cent. of the eggs were impregnated. The rate of 
development compared with the normals is given in the table below: 
