272 THE CELL 



migratory and stationary nuclei of the primary division spindle 

 coalescing, whilst the corresponding structures in the microgamete 

 are, as it were, paralysed, and, instead of fusing and developing 

 further, degenerate and become dissolved, like the fragments of 

 the chief nucleus and the subsidiary spindles. 



In this manner the microgamete loses its independence and 

 individuality, and becomes gradually absorbed into the macro- 

 gamete, increasing the size of the latter. 



Thus, in consequence of the stationary mode of life of Vorticella, 

 a peculiar sexual dimorphism has developed, resulting in the ab- 

 sorption of the smaller of the conjugating individuals, after it has 

 functioned to a certain extent as a male element in fertilising the 

 macrogamete. However, the resemblance to ova and spermatozoa 

 is not complete, although both in Vorticella and Paramasclum 

 fertilisation commences with the interchange of nuclear material, 

 and only results later on in the formation of a single effective 

 individual. 



4. The various forms of sexual cells ; equivalence of participating 

 substances during the act of fertilisation ; conception of male and 

 female sexual cells. Having shown in various instances, that the 

 course of the process of fertilisation, and especially the behaviour 

 of the nucleus during the process, is essentially uniform in animals, 

 plants, and Protozoa, we will now proceed to state more clearly a 

 difference which can be perceived in the cells participating in the 

 act of fertilisation in most organisms, and to point out the im- 

 portance of this difference. It consists in the unequal size and 

 form of male and female germinal cells. The larger, stationary, 

 and hence receptive cell, is called the female; the male cell, on 

 the contrary, is much smaller, often extremely minute ; it is either- 

 motile, approaching the egg-cell actively by amoeboid movements 

 or by means of flagella, or so small that it is conveyed passively 

 through the air or water to the egg-cell. 



What is the importance of this difference ? Is it an essential 

 product of the process of fertilisation, or is it brought about by 

 causes of a subsidiary and secondary nature, due to incidental and 

 secondary causes ? It is of the greatest importance, in order to 

 decide this question, to determine in what substance and in what 

 portion of the two sexual cells this variation manifests itself. 



Each cell consists of protoplasm and nuclear substance. Of 

 these the amount of protoplasm present in the sexual cells may 

 vary considerably, as may be immediately recognised by their ap- 



