The Process of Heredity 553 



type of differentiation have been established, that the influence of 

 the spermatozoon begins to make itself felt. " In the present work 

 I believe that the evidence shows that the influence of the sperma- 

 tozoon is probably immediate and becomes distinctly measurable 

 long before gastrulation. 



Exclusive versus Blended Inheritance 



Are there any examples of exclusive inheritance in the present 

 work ? A pure maternal character, such as the rate of early 

 cleavage, might be termed a dominant character, but if we admit 

 it to be such, we have not far to go in search of a physical explana- 

 tion of this dominance. 



Nearly all of the characters observed may be classed as exam- 

 ples of blended inheritance of one sort or another. The only 

 characters that cannot be thus classified, but seem to be akin to 

 exclusive inheritance are: 



1 The size of the hybrids of both strains on hatching. The 

 size of the M hybrids at the period of maximum development, 

 which is the equivalent of the stage of hatching in the other strains, 

 is on the average that of the smaller species, F. heteroclitus, 

 although the hybrids have developed within eggs of F. majalis, 

 the larger species. The H hybrids are on the average only equal 

 in size to the F. heteroclitus parent at the same period. The 

 character of size on hatching might be called a dominant F. hetero- 

 clitus character, for all strains containing F. heteroclitus are of 

 approximately equal size on hatching (see Plate V). 



2 The color pattern on head and body of both reciprocal 

 crosses is, at a period shortly before and after hatching (in M 

 hybrids at the period of maximum development) practically 

 identical with that of the H pure. F. heteroclitus might then 

 be called dominant with regard to the color pattern at this devel- 

 opmental period (see Plate V). 



Another kind of inheritance occurs, which is neither exclusive nor 

 blended, but seems to be a sort of an exaggeration of exclusive in- 

 heritance, if we may be pardoned the expression. Cases occur in 

 which the hybrids carry certain characters to extremes, showing 

 them to a more marked degree than either parent species. We 



