346 THE CELL 



greater in volume than the total substance of a spermatozoon ; 

 hence protoplasm cannot be the idioplasm. Only one substance 

 fulfils all the necessary conditions, namely, the nuclear substance. 

 The study of the phenomena of fertilisation in the animal and 

 vegetable world proves this irrefutably. 



As was described in chapter seven, the essence of the process of 

 fertilisation consists in this, that the sperm and egg nuclei, i.e. one 

 nucleus derived from the spermatozoon, and one derived from the 

 egg-cell, each accompanied by its centrosome, place themselves in 

 contact, and, fusing together, form a germ-nucleus, from which 

 subsequently, one after another, all the nuclei of the developed 



( organism are obtained by repeated divisions. In Ciliata, two 

 individuals only lay themselves alongside of each other for a short 

 time, so as to exchange migratory nuclei, each of which subse- 

 quently fuses with the stationary nucleus of the other organism. 



As far as the most careful observation shows, the egg and 

 sperm nuclei contribute exactly equal quantities of material to- 

 wards the formation of the germ-nucleus, that is to say, equal 

 quantities of nuclein, and of polar substance, which I include 

 amongst the nuclear substances. 



Fol (VII. 14) has proved the equivalence of the polar substance, 

 which is contributed by the two conjugating individuals, whilst 

 the observations of van Beneden (VI. 4b) upon the process of 

 fertilisation, as seen in Ascaris megalocephala, demonstrate irre- 

 futably the equivalence of the nuclein so obtained. 



\Ve, therefore, draw the following important conclusion from 

 the facts observed during the process of fertilisation : since in 

 fertilisation the nuclear substances (nuclein and polar substance) 



^ are the only materials which are equivalent in quantity, and which 

 unite to form a new fundamental structure, the germinal nucleus, 



\ they alone must constitute the hereditary mass which is transmitted 

 from parent to child. We cannot at present decide what is the 

 exact relation borne by the nuclein and the polar substance to the 

 idioplasm. 



2. The equal Distribution of the multiplying Hereditary Mass, 

 amongst the Cells, proceeding from the fertilised Egg. We are 

 obliged to assume that the multiplying hereditary mass is evenly 

 distributed amongst the descendants of the egg-cell, when we 

 consider the various phenomena of reproduction and regeneration ; 

 for instance, the circumstance that each new organism produces 

 numerous egg or sperm cells, which contain the same hereditary 



