466 



H. H. NEWMAN 



2 hours 



5 hours 



20 hours 



2 days 



3 hours 



6 hours 

 10 hours 



2 hours 

 4 hours 



20 hours 



2 days 



TABLE 8 



Hybrids between Cyprinodon 9 X ^. heteroclitus c^ 



A large proportion of eggs cleaving and in 4- to 8-cell stages ; no 

 signs of polyspermy 



A great variety of cleavage stages, from 8 to more than 32 cells, 

 for the most part regular or nearly so 



A few embryos have reached the end of the cleavage period and have 

 started to form germ rings. The majority have begun to dis- 

 integrate at the end of the cleavage period 



All those that were developing at 20 hous now dead, several hav- 

 ing reached a condition in which the germ ring was about half 

 around the yolk and a fiat embryonic shield with no visible em- 

 bryonic axis had been differentiated. This cross is more success- 

 ful than the reciprocal cross, but less so than when the same 

 eggs are fertilized by the sperm of F. diaphanus 



TABLE 9 

 Hybrids between F. majalis 9 X Cyprinodon c? 



About 25 per cent of eggs cleaving and in 2- and 4-cell stages, many 



irregular and some evidently polyspermic 

 Only a very few eggs alive, others show various degrees of cyto- 



lysis 

 All dead and disintegrating after reaching advanced cleavage stages 

 Note: Another cross of these two species gave even less success 

 than that here indicated 



TABLE 10 



Hybrids between Cyprinodon 9 X F. majalis cf 



Nearly all eggs cleaving in an apparently perfectly normal manner. 



A wide range of cleavage stages ranging from 8 to 32 cells. Those 

 that are much retarded look unhealthy 



All but two embryos dead in advanced cleavage stages. The two 

 that are alive are in early germ ring stages, showing flat embry- 

 onic shield. Both are much less advanced than control 



The two embryos that were alive at 20 hours are now dead without 

 having made much progress since the last observation. This 

 cross is more successful than the reciprocal, but less successful 

 than either of the other Cyprinodon egg hybrids 



