278 THE CELL 



mass and composition. Only we must understand by the ex- 

 pression male or female nucleus nothing more than a nucleus 

 derived from a male or female cell. In the same way, in In- 

 fusoria, the migratory nucleus may be termed male and the 

 stationary nucleus female, in the sense of the above definition, 

 since the former seeks the latter. 



This difference, which has developed in sexual cells for the 

 purpose of division of labour, and to fit them for their special 

 work, is repeated in the whole organic kingdom, whenever the indi- 

 viduals in which the male and female sexual cells develop differ 

 from one another in sexual characteristics. In all the arrange- 

 ments referring to sex, one and the same object is aimed at : 

 measures are taken on the one hand to facilitate the meeting of 

 the sexual cells, and on the other to arrange for the nourishing 

 and protection of the egg. The one organisation we call male, 

 and the other female. All these relationships are secondary, and 

 have nothing to do with the process of fertilisation itself, which 

 is a true cell phenomenon. 



Fertilisation is an union of two cells, and, above all, a fusing 

 of two equivalent similar nuclear substances, which are derived 

 from two cells, but it is not a combination of sexual opposites, for 

 the differences depend solely upon structures of subsidiary import- 

 ance. 



The truth of the above law may be still more clearly demon- 

 strated, if we compare the generative processes throughout the 

 whole organic kingdom, and thereby endeavour to determine how 

 the differences have gradually developed between the cells which 

 unite for the purpose of fertilisation. Amongst unicellular organ- 

 isms and plants, we find innumerable instructive examples of the 

 elementary and primitive forms of sexual generation and of the 

 origin of sexual differences in the plant and animal kingdoms. 



5. Primitive and fundamental modes of sexual generation and 

 the first appearance of sexual differences. The study of the 

 lowest organisms, such as Nuctiluca?, Diatomaceas, Gregarinse, Con- 

 jugate, and other low Alga?, shows that in many of them the con- 

 jugation of two individuals occurs in regular cycles, and this we 

 must regard as a process of fertilisation. 



In Noctlluca conjugation commences by two individuals, 

 which are of the same size, and do not differ from one another in 

 any respect, placing themselves side by side, with their mouth 

 apertures opposite one another, and beginning to fuse, whilst their 



