344 THE CELL 



assume that the idioblasts are arranged in a constant regular 

 manner. This portion of the theory is the most difficult to under- 



stand. 



In the above, certain logical principles for the formation of a 

 physiological molecular theory of generation and heredity have 

 been deduced, in accordance with Nageli's views. We must leave 

 the proof of the correctness of these assumptions to future ob- 

 servers and experimenters, who will thereby establish the relation 

 between the theory, and the facts which are perceptible to our 

 senses. The physiological idea of the creation of the organic 

 world from elementary units, and of the essential agreement in 

 the structure of plants and animals, have been of real service in 

 building up the cell and protoplasm theories; in a similar manner 

 we must hope to obtain a corresponding position for the theory 

 of heredity. Several attempts have already been made in this 

 direction, connected with the observations made upon the fertili- 

 sation in animals, plants, and Infusoria. 



III. The Nucleus as the transmitter of Hereditary 

 Elemental Germs. The hypothesis that the nuclei are the 

 transmitters of the hereditary properties, was suggested to both 

 Strasburger and myself by the study of the process of fertilisation 

 and of the theoretical considerations connected with it ; thus we 

 have assigned to the nuclear substance a function, which is 

 different from that of protoplasm. A short time before, Nageli 

 had been compelled, solely on logical grounds, to assume, that two 

 different kinds of protoplasm were present in the sexual cells, the 

 one sort which occurs in exactly equal proportions in the egg and 

 sperm cell, conveying the hereditary properties, and the other, 

 which is stored up in great quantities in the ovum, functioning 

 chiefly as a nutritive medium. He calls the first idioplasm, and 

 the second somato plasm, and assumes that the former is more 

 solid in consistency, the micellae being regularly arranged, whilst 

 the latter contains more water, and hence its micellae are less 

 closely united. He imagines that the idioplasm is extended like 

 a fine network throughout the whole cell body. 



If it be admitted, that the assumption of a separate idioplasm is 

 logically justifiable, it cannot be denied that the nuclear substance 

 probably constitutes the hereditary mass. 



Further, by means of this theory, a practical interpretation has 

 been given to Nageli's deduction, which was based simply upon 



