472 H. H. NEWMAN 



have been observed in any of the numerous experiments deahng 

 with F. majahs egg hybrids that have been under my observa- 

 tion during the last eight years. Moenkhaus, moreover, agrees 

 with me that these hybrids never hatch. 



c. Inter-generic crosses 



It is possible to produce six crosses between Cyprinodon and 

 the three species of Fundulus, as shown in tables 5 to 10. In 

 no case is the cross successful in the sense that a larva or even 

 an advanced embryo is produced. None of the hybrids go far 

 enough to show specific characters, but all go through the cleav- 

 age period more or less normally and some develop through the 

 period of gastrulation and begin to show embryonic differentiation. 



The six crosses may be significantly arranged in the order of 

 their success in development, as follows: 



1. Cyprinodon 9 X F. diaphanus cf . A small percentage of 

 the embryos go practically through the period of gastrulation and 

 begin to show the rudiments of embryonic differentiation. 



2. Cyprinodon 9 X F. heteroclitus d". A large proportion of 

 the eggs go through to the end of the period of cleavage in a 

 nearly normal manner and a few advance to a stage in which the 

 germ ring has covered about one-third of the yolk and a flat 

 embryonic shield is developed. Here the stoppage occurs in the 

 midst of the process of gastrulation and before the embryonic 

 axis is established. 



3. Cyprinodon 9 X F. majalis d". A few embryos go through 

 the cleavage period and show the beginnings and early steps in 

 gastrulation, a well defined germ ring with flat embryonic shield 

 being formed, as in figure 11. 



4. F. diaphanus 9 X Cyprinodon cf. Many embryos go 

 through the period of cleavage and a few of them form a germ 

 ring but get no further, the most advanced condition being like 

 that shown in figure 9. 



5. F. heteroclitus 9 X Cyprinodon cT. Many embryos develop 

 through the cleavage period but fail to begin gastrulation, as 

 indicated by the absence of any trace of a germ ring. 



