70 Chemical Basis of Genus and Species 



It is not impossible that protamines and histones 

 might be found to act as specific antigens if they 

 were not so toxic. The positive results which Taylor 

 observed after injection of the sperm might have 

 been due to the proteins contained in the tail of the 

 spermatozoa, which in certain animals at least does 

 not enter the egg and hence can have no influence on 

 heredity. 



It is thus doubtful whether or not any of the con- 

 stituents of the nucleus contribute to the determination 

 of the species. This in its ultimate consequences 

 might lead to the idea that the Mendelian characters 

 which are equally transmitted by egg and spermatozoon, 

 determine the individual or variety heredity, but not 

 the genus or species heredity. It is, in our present 

 state of knowledge, impossible to cause a spermatozoon 

 to develop into an embryo, 1 while we can induce the 

 egg to develop into an embryo without a spermatozoon. 

 This may mean that the protoplasm of the egg is the 

 future embryo, while the chromosomes of both egg and 

 sperm nuclei furnish only the individual characters. 



1 Loeb, J., and Bancroft, F. W., Jour. Exper. Zool., 1912, xii., 381. 



