252 EDITH PINNEY 



Menidia menidia notata 9 X Ctenolahrus adspersus cf 



# 



One experiment in which the eggs of Menidia menidia notata 

 were fertihzed with the sperm of Ctenolabrus gave larvae which 

 hatched. Both of these were Hke the pure Menidia embryos. 

 One was healthy and one, evidently hindered by a large yolk 

 sac, could not swim well, but lay on its back for most of the time. 

 No attempt was made to see how long these embryos might live. 

 Newman has listed this cross among those in which development 

 does not go beyond the gastrulation stages, but in view of his 

 experience in regard to the different outcome of the same cross 

 at different times, he emphasizes his conviction that such a list 

 can only be tentative. 



The most important stages of this cross which have been stud- 

 ied are third-cleavage stages. Eggs in all of the mitotic phases 

 were exammed and some of the typical occurrences are seen in 

 figures 80 to 88. In figure 80 a metaphase is shown in which 

 nuclear material is being pushed out of the nucleus toward the 

 inner boundary of the cell which marks the last cleavage plane. 

 This is the same thing which was seen to occur in the cross 

 Fundulus 9 X Ctenolabrus cf. It was observed only once 

 among many eggs in the same stage, in which conditions were to 

 all appearances normal. 



Figures 81 to 85 illustrate the most frequent condition during 

 the anaphase. In figures 81 and 82 bodies which are supposed 

 to be undivided chromosomes are on their way to the poles. 

 Figures 83 and 87 show respectively a mid-anaphase and a later 

 telophase. A comparison of these figures leads to the conclusion 

 that lagging material present at the equator in the early stages of 

 mitosis may still be at the equator when the nuclear elements 

 gathering at the two poles are undergoing their metamorphosis 

 and are forming vesicles. Another telophase in which distinct 

 chromosomes are lagging at the equator is shown in figure 88. 

 It does not seem possible that such an abnormal delay in the divi- 

 sion of some of the chromosomes can result in the usual precise 

 distribution of chromosomes to the two poles. 



