198 MICHAEL F. GUYER. 



additional hybrids between Tetrao tetrix and Tetrao urogallus, 

 of which 40 are male and 8 female. Again, page 573, he lists 

 20 hybrids of Lagopus albus- and Tetrao tetrix, of which 13 are 

 male and seven are female. 



As to the general bearing of these facts upon any one of the 

 numerous theories of sex-determination, the writer does not feel 

 disposed to dogmatize, although certain suggestions present them- 

 selves. For a general and unbiased statement of our present 

 knowledge regarding the question of sex-determination, the 

 reader may consult the recent publications of Thomson 1 or of 

 Morgan. 2 



Both of these writers agree that when all the evidence is con- 

 sidered it does not seem improbable that the conditions which 

 regulate the development of sex may be different in different kinds 

 of animals. Regarding the sex-determining influence of nutri- 

 tion and temperature, either directly on the developing organism 

 or through its parents, Thomson points out that while the evi- 

 dence in any given case is inconclusive, still when all the cases 

 are taken together, " they have a certain cumulative suggestive- 

 ness which would warrant further experiment particularly as 

 regards the lower animals and the indirect influence on offspring 

 through the parents" (1908, p. 490). 



In general, where the experiments tend to show that nutrition 

 is a factor after the period of fertilization, it has been the produc- 

 tion of females that was supposedly favored by such increased 

 nutrition ; the question being apparently one of increased con- 

 structive metabolism. It would follow that anything tending to 

 retard or hold at a low ebb the constructive phases of metabolism, 

 especially during early embryogeny, would be inimical to the pro- 

 duction of females. Now in the case of hybrids, and particularly 

 those from widely separated parents, there would in all proba- 

 bility be more or less default in the metabolic processes because 

 of the incompatibilities which must necessarily exist between two 

 germ-plasms so dissimilar. It seems not improbable, therefore, 

 that this might be the determining factor in the production of an 

 excess of males in the case of such hybrids. 



1 Thomson, J. Arthur, "Heredity," London, 1908. 



2 Morgan, T. H., "Experimental Zoology," New York and London, 1907. 



