456 H. H. NEWMAN 



the rate of the sperm species is faster or slower than the egg 

 species," that Bancroft takes the position that: 



As regards the rate of development of the embryos my observations 

 confirm those of Newman on most points. The development of the 

 F. heteroclitus egg hybrid was shown to be slower than that of its 

 maternal parent; and the development of the F. majalis egg hybrid, 

 during the early stages, was faster than that of the pure F. majalis. 

 After hatching the F. heteroclitus egg hybrid seemed more vigorous 

 and grew faster under like conditions than either of the pure forms. 



It is somewhat strange that Moenkhaus failed to note these 

 facts for he must have performed the experiment a number of 

 times. Bancroft's paper adds materially to our knowledge of 

 the heredity of pigment in teleost hybrids. His analyses of these 

 processes is more nearly adequate than that of any other writer. 

 In the general discussion of new data I shall have occasion to 

 come back to this paper for more detailed treatment. 



This then is the history of the development of our knowledge 

 of heredity in teleost hybrids. From this array of facts and 

 theories it is possible to extract certain well-defined problems 

 and unsettled questions, which it is my intention to put to the 

 test of further experiment. A list of some of the more important 

 questions is herewith introduced in order to clarify the issue and 

 to focus the attention of the reader upon the problems involved. 



1. At what point in the development of an embryo does the 

 sperm begin to exercise an hereditary as opposed to a merely 

 chemical effect upon the character of development? 



2. Is the rate of cleavage 'inherited,' in a strict sense, or is it 

 merely a function of egg size and of yolk content? 



3. Is the effect of foreign sperm to be looked upon as neces- 

 sarily deleterious, and hence toxic, or is the effect bad only when 

 there arises so pronounced a disharmony of the two engrafted 

 ontogenies that no blending or compromise can be reached? 



4. Is it true that all characters concerned with or resulting 

 from the rate of development are inherited in the blended fash- 

 ion? Is rate of development strictly an hereditary character? 



5. Is the degree of success in the development of hybrids in 

 any way closely correlated with the nearness of relationship of 



