260 EDITH PINNEY 



that they would ever produce mature germ cells, since there 

 would be much hindrance to a normal synapsis preceding the 

 reduction divisions. 



On this basis, the character of the recessiveness shown in hetero- 

 geneous crosses is not comparable to that displayed in some inter- 

 varietal crosses. 



The occurrence of embryos showing paternal inheritance has 

 been advanced as proof that the spermatozoon does exercise some 

 influence upon the development of the egg. All of the paternal 

 characters : o far recognized as attaining their full development 

 in fish embrj^os are characters of rather an unimportant type, 

 such as chromotophores, which would not be expected to have 

 much effect in the inhibition of development. It is conceivable 

 that the factors which determine chromatophores may differ 

 very slightly in degree in different genera as compared with 

 factors which determine characters of a moro fundamental nature 

 — size, body form, etc.- — and in so far as the interaction between 

 the parental characters for chromatophores are ' oncerned, we 

 may be dealing with a phenomenon common to all fish hybrids, 

 homogeneric as well as heterogeneric. 



The appearance of paternal chromatophores indicates the 

 retention of the paternal chromosomes. Whether the patho- 

 logical features of such embryos are to be regarded as due to the 

 interaction of paternal and maternal chromatin is uncertain. 

 They can be accounted for by the mechanical hindrances to 

 development shown to exist in some crosses. 



In general the facts obtained from this study confirm the view 

 of the Hertwigs as to the»factors which are responsible for the 

 results of hybridization, but they indicate that the relative 

 importance given by the Hertwigs to these factors should be 

 reversed. The apparently anomalous development of fish 

 hybrids does not depend, first, upon the combination of idio- 

 plasms, and, second, upon the interaction of the idioplasm of the 

 sperm and the cytoplasm of the egg, but, first, upon the effect 

 of the cytoplasm on the sperm, and, second, upon the reaction 

 between the two germ nuclei. We must add to these a third 

 factor upon which the action of these first two depends, namely, 



