INTRODUCTION 29 



nucleus ; for. as has already been indicated, and will subsequently 

 be shown more clearly, this substance can hardly be stored up 

 in two different places, seeing that a very complicated apparatus 

 is required for its distribution : a double apparatus would cer- 

 tainly not have been formed by nature if a single one suffices 

 for the purpose. Only as long as the phenomena of heredity 

 and the meaning of these phenomena are still far from being 

 known, is it possible to hold such opinions as that which pre- 

 supposes the distribution of the hereditary substance amongst 

 both cell and nucleus. As soon as a further insight into these 

 processes is obtained, it will no longer be possible to doubt that 

 the structure of the hereditary substance must be so complex 

 that we can only wonder how it could ever have been developed 

 at all. We know that the nucleus contains a substance which, 

 even with the imperfect means of observation at our disposal, is 

 seen to be extremely complex, and that it becomes modified in 

 a^vefynrernarkable manner after every cell division, only to be 

 again transformed at the approach of the following division. We 

 can, moreover, observe that the cell is provided with a special 

 apparatus which evidently enables it to halve this substance very 

 accurately. The statement that tliis substance is the hereditary 

 substance can, therefore, hardly be considered as an hypothesis 

 any longer. 



It has also been supposed that fresh evidence against the 

 view that the chromosomes are the hereditary substance, has 

 been furnished by the recent observations of Fol * and Guignard,t 

 which prove that the centrosome and its ' sphere of attraction,' — 

 which belong to the cell-bodyT and constitute the apparatus for 

 division, — pass into the ovum along with the sperm-nucleus in 

 the process of fertilisation. Suppose I take two heaps of grain 

 from different places, and load them on two carts, harness a 

 horse to each cart, and drive them to the same place ; does this 

 prove that the horses consist of grain? They are merely the 

 means by which the grain is transferred from one place to 

 another, just as the centrosomes are the means whereby the 

 sperm-nucleus is transferred to the ovum : whether they are any- 



* ' Le Quadrille des Centres,' Archiv. Sc. Phys. et Nat., Geneve, 15 

 Avril 1891. 



t 'Sur I'Existence des Spheres Attract! ves dans les Cellules V6g6tales,' 

 Compt. Rend. Sc, 9 Mars 1891. 



