410 H. H. NEWMAN 



situation is entirely different. All cytological studies of Teleost 

 hybrids of suborder width show that the paternal chromosomes 

 retain their specific size, shape, and number, and are distributed 

 to the blastomeres nearly or quite normally during the cleavage 

 period. That occasional irregularities in chromosomal distribu- 

 tion occur is seen in this and other types of hybrid in which 

 there occur numerous eggs in which pronouncedly irregular 

 cleavage occurs. Such embryos die in early stages of cleavage 

 or before embryonic differentiation begins. It seems certain, 

 therfore, that in all of those embryos that reach an advanced 

 embryonic stage the chromosome distribution (both maternal 

 and paternal) has been at least fairly normal. Moenkhaus 

 found that the paternal chromosomes were still normal in their 

 distribution in advanced embryonic stages in the Fundulus X 

 menidia cross, a cross of the same width as that between Fundulus 

 and the mackerel. If, therefore, the paternal heredity materials 

 cooperate during the developmental process with the maternal, 

 it seems logical to expect them to function in heredity. It is 

 hardly conceivable that the chromosomes, which are living en- 

 tities, should be growing, dividing, and being distributed from 

 cell to cell in cleavage and later development, unless they are 

 functioning, and if they are functioning, how else can they 

 function than in the expression of the changes we speak of as 

 differentiation and heredity? 



In view of these considerations, we must seek some other 

 explanation of the pure maternal appearance of the most suc- 

 cessful Teleost hybrids. It is my belief that the occasional 

 occurrence of a hatching larva in such a cross as that between 

 Fundulus and mackerel is to be interpreted as a case of early 

 and complete recovery from an initial inhibiting agent. Though 

 the foreign sperm fertilizes the egg and cooperates with it in 

 development and heredity, it must also introduce some materials 

 that are inimical to normal development. This would seem only 

 likely from what we know of the high degree of specificity of 

 protoplasmic materials. In a few cases the egg materials are 

 able either to transform, absorb, or in some other w^ay to neutral- 

 ize these foreign elements so that they have little or no harmful 



