464 



H. H. NEWMAN 



TABLE 4— Continued 



b. Crosses between two genera 



TABLE 5 

 Hybrids between F. diaphanus 9 X Cyprinodon variegatus c? 



3 hours About half of the eggs fertilized and in 2- and 4-cell stages, a few 



obviously polyspermic, others indistinguishable from control 

 5 hours Advanced cleavage of regular character in the majority of develop- 

 ing eggs, but polyspermic eggs show great irregularity and con-' 

 siderable cytolysis 

 18 hours I All monospermic eggs normal in appearance but less advanced than 



j control, the beginnings of cytolysis in a few blastodiscs 

 24 hours I All eggs show cytolysis of marginal cells of blastodisc, indicating 

 that development has ceased and disintegration has set in. The 

 limit of development in this cross seems to be the end of the 

 cleavage period although a few embryos have begun to show the 

 first indications of a germ ring, indicating that gastrulation or 

 germ layer differentiation had begun but could progress no 

 further 



