BOVERI'S EXPERIMENT 39 



Note on Boveki's Expekiment on the Egg or the Sea-Uechin. 



Weismann has expressed the opinion that the combination of the two 

 sperm nuclei would be capable of producing the same results as the com- 

 bination of an ovum nucleus and a sperm nucleus, and has based his opinion 

 on Boveri's experiment on the egg of the sea-urchin. Weismann's view 

 is probably correct, and in any case we may safely affirm that the sperm 

 nucleus is able to replace the ovum nucleus. It is probable that in Boveri's 

 experiment only a single sperm nucleus was in activity. The possibility 

 of the sperm nucleus fecundating the denucleated ovum is consistent 

 with what we have already concluded — that there is no organic difference, 

 but rather organic identity, between the spermatozoon and the ovum. 

 The spermatozoon cannot survive independently of the egg, because it 

 lacks nutritive substance. On the other hand, the egg either lacks a 

 centrosome as the result of the changes which occur in maturation, or else 

 its centrosome is in a state of degeneration. Seeing that the spermatozoon 

 possesses a centrosome and aU the essential properties of the ovum and 

 that the cytoplasm of the denucleated ovum is at its disposal, there would 

 be reason for surprise if the result of Boveri's experiment had been other 

 than it was. 



Note cgncbbjjing the Detekminants. 



It must be observed that external conditions have also an influence on 

 the determinants. The determinants are, as we have seen, living unities, 

 and consequently they respond differently to different stimuli. Thus, 

 imder normal conditions, the determinant produces a normal determinate ; 

 but under abnormal conditions, in so far as these do not exclude all possi- 

 bility of development, the determinant will produce an abnormal deter- 

 minate. The experiments of Herbst on the egg of the sea-urchin have 

 shown that when certain components of the sea-water are replaced by other 

 chemical substances, the structure of the larva differs profoundly from 

 the normal condition. It must not be forgotten that the great majority 

 of the finished parts of an organism are not determined by a single deter- 

 minant, but by all the determinant complexes which have formed, during 

 the developmental process, the many cells which share in the biogenetic 

 history of a given part. There are no special determinants of an aquiline 

 or a hooked nose, but many determinant complexes shared in forming 

 the various ceUs which led up to the development of the nose in the finished 

 organism ; and these successive complexes of determinants have so formed 



