DEVELOPMENT IN CROSS-FERTILIZED EGGS 407 



in which the egg of Ctenolabrus was used normal mitotic divi- 

 sion was the rule. The eggs of Stenotomus, Fundulus, and 

 Menidia, however, when fertiUzed with the sperm of Ctenolabrus 

 showed the typical abnormality duriag the anaphase cleavage 

 which is described above. It w^as, therefore, a matter of interest 

 to find a cross wdth this species in which the reciprocals were 

 alike in their early mitotic behavior, as is the case in the cross 

 between Ctenolabrus and Prionotus. The behavior is normal 

 in both eggs. Nothing earher than second-anaphase figures of 

 both of these crosses w^ere observed. From much observation 

 of other crosses I feel convinced that the second cleavage mitosis 

 resembles the first verj'^ closely, and that therefore in these recip- 

 rocal crosses no elimination of chromatin or abnormahties in 

 mitosis occur during the first cell division. 



I thought that perhaps some evidence on this point might 

 be gained from a study of polar groups of chromosomes after 

 actual division had occurred. With this in mind, I attempted 

 to estimate the chromosomes to be expected in polar groups and 

 then determine whether second-anaphase groups fulfilled this 

 expectation. The sources of error in such a study are numerous, 

 and the estimates that I have made can only claim to be approxi- 

 mate. Counts of both polar and lateral views of anaphase 

 groups place the number of chromosomes in the normal Priono- 

 tus egg near fifty. My earlier counts of the species Ctenolabrus 

 give indications that the number there is about forty-four. We 

 should then expect between forty-five and fifty in the hybrid 

 eggs. Actual counts are as follows: 



r.. , . ^ -n • X 52 53 56 49 



Ctenolabrus 9 X Prionotus d^, — , — , — 



51 56 59' not counted 



Prionotus 9 X Ctenolabrus d^, — , ^, — . 



58' 50' 50 



The unexpectedly large number here is probably due to the 



sectioning of single chromosomes. No entire spindles or even 



single polar groups were found. Obviously, such material is 



not adapted to accurate counting. As evidence, while it may 



show that no great elimination of chromosomes has occurred, 



as regards irregular distribution of chromosomes it has no value. 



