THE CONSEBVATION OF LIFE 231 



of a specially formed cilia- wreath. How long this free life lasts 

 depends upon many accidents. If the little ' microgamete,' as it is 

 called, encounters on its travels a normal individual of the same 

 species, a so-called macrogamete, it attaches itself at once to its 

 side and fuses with it into one uniform whole. And as the cell- 

 body, so their two nuclei unite. Only the discarded pellicle of 

 the microgamete, which is not included in the union, is the external 

 sign that conjugation has taken place. 



At first the fertilized Vorticella differs from an ordinary macro- 

 gamete by the formation of its nuclear apparatus, but by repeated 

 division descendants are produced which have once more a normal 

 appearance and are ready for a new conjugation or we must 

 now, perhaps, more accurately use the term fertilization. 



If we cannot know with certainty what caused in the bell- 

 animalcule this division of labour i.e., the formation of male 

 ' wander-spores,' it is, nevertheless, perhaps not quite futile to 

 make at any rate an attempt to explain the probable causes of 

 these differentiations. I have already pointed to the great 

 importance of the conjugating-process, and we saw that only an 

 exchange of nuclei between non-related individuals can guarantee 

 the intended result. The large majority of Vorticella are fixed to 

 the ground. Is it not then obvious that in most cases conjugation 

 is practically impossible, or at any rate most difficult? It is true 

 that in the colony-forming species numerous individuals are pro- 

 duced together in a small space, but since they are all blood- 

 relatives union between them cannot take place. Thus the 

 formation of free-moving germs which separate from the mother- 

 stem and are able independently to seek another strange stem, 

 seems the only possible means to bring about conjugation, in 

 spite of a sedentary mode of life. 



Why the * wander-spores ' are so differently shaped, why 

 there is a differentiation into two sexes, and, in the act of fecun- 

 dation, why the union of both sexes becomes permanent instead 

 of the animalcules contenting themselves as heretofore with a 

 mere exchange of their nuclear substance our hypothesis has so 

 far left unexplained. Yet the reason for this new phenomenon 

 is not difficult to perceive : it is the same circumstance which 

 conditions the difference in the formation of ovum and sperma- 

 tozoon in the higher animals. 



