THE GERM-PLASM 45 



which is differentiated into the cell-substance, as well as the 

 idioplasm contained in the nucleus. It will be shown subse- 

 quently in what manner these two kinds of protoplasm differ as 

 regards their constitution, and I will only remark here that the 

 idioplasm must have a far more complex structure than the mor- 

 phoplasm. The latter, as the cell-substance of a muscle or 

 gland-cell shows, can assimilate, grow, and also divide, but it is 

 not able to change into anything different from itself. The 

 idioplasm, oh the other hand, is capable of regular change dur- 

 ing growth ; and ontogeny, or the development of the individual 

 in multicellular organisms, depends upon this fact. The two 

 first embryonic cells of an animal arise from the division of the 

 ovum, and continually give rise to differently constituted cells 

 during the course of embryogeny. The diversity of these 

 cells must, as I have shown, depend on changes in the nuclear 

 substance. 



It now remains to be considered how we are to imagine this 

 capacity on the part of the idioplasm for regular and spontane- 

 ous change. The fact in itself is beyond doubt, when once it is 

 established that the morphoplasm of each cell is controlled, and 

 its character decided, by the idioplasm of the nucleus. The reg- 

 ular changes occurring in the egg-cell and the products of its 

 division in each embryogeny must then be referred to the corre- 

 sponding changes of the idioplasm. But what is the nature of 

 these cha?iges, and how are they brought about / 



2. The Control of the Cell 



In order to answer the question which has just been asked, it 

 will be necessary to consider the manner in which the idioplasm 

 of the nucleus determines the characters of the cell. At present 

 we only know that the idioplasm consists of a large number of 

 different biophors of various kinds. To exert a determining 

 influence on the minute structure of the cell-body and on the 

 chemical composition of its different components, it must either 

 be capable of exerting an emitted influence (' Fernwirkung ') or 

 else material particles must pass out of the nucleus into the cell- 

 body. 



Strasburger * has endeavoured to prove a dynamical effect of 



* E. Strasburger, ' Neue Untersuchungen iiber den Befiuchtungsvorgang 

 bei den Phanerogamen," 1884, p. iii. 



