I So DYNAMICS OF LIVING MATTER 



forms no skeleton. If the egg of a sea urchin is fertilized by the sperm 

 of a starfish, those larvae that live long enough develop invariably into a 

 pluteus.* It would be interesting to ascertain whether the hybrid 

 larvae produced from a starfish egg by the fertilization with a sea urchin 

 spermatozoon ever form a pluteus larva. These data also indicate 

 that the statement that fertilization consists in the fusion of two nuclei 

 does not cover all the facts. 



As far as the adult is concerned, it seems that, as a rule, spermato- 

 zoon and egg have an equal share in the transmission of the hereditary 

 qualities. Mendel states that in the case of the hybridization of two 

 species of peas, a and b, the results were the same, whether the pollen came 

 from the species a and the egg from the species b, or vice versa. We 

 shall see later on that the early embryo is to a certain extent predeter- 

 mined in the protoplasm of the egg. This makes it natural that these 

 early stages should depend upon the egg, and not upon the spermato- 

 zoon. As far as the adult is concerned, the protoplasm has to be formed 

 by the taking up of food, and the chemical as well as the subsequent 

 physical changes which the material undergoes will be under the in- 

 fluence of the catalytic agencies of both the egg and the spermatozoon. 



We do not know which circumstances in the sexual cells determine 

 the hereditary effects, although one would naturally think first of definite 

 chemical compounds as the bearers of hereditary qualities. The greater 

 part of the spermatozoon, namely, the head, consists of a salt whose 

 acid is nuclcinic acid, whose base in some fishes and starfish is pro- 

 tamine, in other forms histones, which latter, however, are closely related 

 to the protamines. In order to decide whether the nucleins or the 

 histones or the protamines are of importance for the hereditary qualities, 

 it would be necessary to decide whether the nuclei of the eggs of one 

 form contain always the same base as that found in the sperm of the 

 same species. This should be expected from the fact that the hereditary 

 influence of egg and sperm is equal in the adult offspring, at least. 

 It seems that the base is not always identical in the egg and sper- 

 matozoon of the same species, and this seems to indicate that the 

 nucleic acid is of more importance for heredity than protamines and 

 histones. Aside from the nuclein we find albumin and globulin, es- 

 pecially in the tail, and in the latter also lecithin, cholesterin, and fat. 

 Miescher believed that in the head of the spermatozoon an iron compound 

 exists. It is impossible to draw any far-reaching inference concerning 

 the nature of the substances which transmit hereditary qualities from 

 these meager data. 



The fact that the spermatozoon contributes just as much to the trans- 



* Loeb, loc. cit. 



