363 



Practically all of the eggs were normally impreguated, a very few of 

 the eggs fell directly into four and six cells. 'I he rate of development was 

 the same as the normals, until the later stages, when the hybrids fell 

 behind, as shown in Table 3. 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 embrj'o. 

 however, does not form in the shield as it should. I have seen many eggs 

 forming the germ ring and embryonic shield 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. 





FUNDULUS 



FuNDULUS 





X 



X 





FUNDULUS. 



Tatjtoglabrus. 



Fertilization. 



9.30 a. m., July 4, 



9.30 A. M., July 4. 



Begin. 2 cells. 



11.17 



11.17 



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 P. M., Julys. 



Vi 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. 



IWiiilopoJahriif! (tdspcvfiiis. 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 : 



