510 MARGARET MORRIS 



there is certainly elimination of paternal chromatin; for in an- 

 other part of the same egg in which these abnormal cells occur, 

 spindles are to be found like those represented in figures 29 to 

 32, in which the Ctenolabrus chromosomes are present. The 

 disturbance is undoubtedly a result of the fertilization with the 

 foreign sperm — we find no such condition in normally fertilized 

 eggs — but we cannot say that it concerns the paternal chromatin 

 alone. It seems, rather, to involve the whole cell, and is probably 

 the cause of the death of many of the embryos and the abnormali- 

 ties of those that survive. Where the cells continue to divide nor- 

 mally they retain the two types of chromosomes. 



It will be seen that the cytological study of these eggs hardly 

 supports Loeb's theory that the function of the sperm in such 

 hybrids is merely that of a parthenogenetic agent. Nor do the 

 conditions agree with those found in Echinoderm hybrids, with 

 the exception of those between the Echinus and Strongylocen- 

 trotus females and the Antedon male. Although up to the 24- 

 hour stage the larvae show no signs of paternal inheritance, it 

 would be hardly safe to say that they were purely maternal in 

 character, if it were not for Loeb's description of later stages of 

 hybrids between these same two species of fish. As he, however, 

 found no paternal characters in these larvae at any time, it must 

 be concluded that the Fundulus egg fertihzed with the sperm 

 of Ctentjlabrus gives purely maternal larvae without elimination 

 of the foreign chromatin. 



SUMMARY 



1. In the cross Fundulus 9 X Ctenolabrus cT the germ-nuclei 

 are closely apphed to each other, but form chromosomes for the 

 first division without having fused. 



2. The chromosomes of the first cleavage spindle are of two 

 types, which correspond respectively to those seen in the nor- 

 mally fertilized eggs of the two species. 



3. Although the foreign chromosomes lag somewhat behind 

 the others in going to the poles, they are all finally included in 

 the daughter-nuclei of the 2-cell stage. 



