30 THE GERM-PLASM 



thing more than this, — i.e.^ whether they contain hereditary sub- 

 stance, — still remains to be proved, and such a conjecture is 

 hardly more probable than that the horses, besides being the 

 means of transport of the corn, should actually consist of corn I 



It might, however, be urged that the transference not only of 

 the hereditary substance or store of primary constituents, but 

 also of the centrosome or //leans of transference of this substance, 

 implies the transference of the rate of cell-division, which is 

 regulated by the centrosome and essentially decides the cell- 

 sequence in the offspring, and which consequently also takes 

 part in heredity. But I consider this also to be an incorrect 

 deduction, because the periods of activity of the apparatus for 

 division must obviously be dependent on the conditions of the 

 cell itself; these conditions, however, apart from nutrition, de- 

 pend on the ultimate specific structure of the cell. As, accord- 

 ing to my view, this structure is impressed on the cell by the 

 nuclear substance, the periodicity of cell-division must also be 

 dependent on the nucleus. The law that only a certain part of 

 the nuclear matter is to be regarded as the hereditary substance 

 appears to me to receive fresh support from all the tnore recent 

 observations* 



Chromatin substance is not only contained in the nucleus of 

 the germ-cells and of the fertilised ovum, but also in all the cells 



* Many seem inclined to regard the process observed b)' Fol, which he 

 described as ' Le quadrille des centres,' as a proof that the centrosomes 

 nevertheless must — or at any rate might — contain a kind of hereditary sub- 

 stance. I believe, however, that this process is quite similar to that which 

 occurs in every nuclear division, except that in fertilisation, — owing to the 

 fact that the first segmentation nucleus receives a centrosome from each of 

 the two conjugating cells, — it is a double, and not a single process. Each of 

 these centrosomes divides and passes to the region of the two poles of the 

 future spindle, just as would occur if only a single centrosome were present 

 in the cells. I should be surprised if this were not the case, and if the 

 centrosome of the egg-cell passed to one pole, and that of the spermatozoon 

 to the other! Guignard is of the opinion that even if the nucleus is of great 

 importance as regards the transference of transmissible qualities, we must 

 nevertheless attribute to the ' spheres directives,' ' le r6ie primordial dans 

 I'accomplissement de la f^condation.' This is true if it only indicates that 

 the beginning of embryonic development depends — as does every nuclear 

 division — on the presence of the apparatus for division. But the view is 

 not thereby refuted that fertilisation consists in the union of two nuclear 

 substances. 



