CONJUGATION OF VORTICELLA 243 



goes two more divisions, each accompanied by a division of 

 the micronucleus, whilst the meganuclei are simply distributed 

 equally among the progeny. The young Vorticellid with three 

 meganuclei behaves similarly, but as there are only three 

 meganuclei to be distributed, only three young forms are pro- 

 duced in the manner shown in the diagram. 



The fate of the original meganuclei of the two gametes has 

 already been alluded to. At a very early stage they are broken 

 up by abstriction into a number of fragments, those of the 

 microgamete being always smaller than those of the macro- 

 gamete. The fragments continue to break up into smaller 

 and smaller pieces which are finally absorbed and disappear 

 altogether. 



One cannot fail to observe that the conjugation of Vorticella 

 is a step further advanced towards a differentiation of sex than 

 in Paramecium. Volvox exhibits a still more marked sexual 

 differentiation, but, whilst it is allied to animal forms, it has 

 all the characters of a plant. Whereas in Paramecium the 

 gametes are similar, the conjugation temporary, and both of 

 the ex-gametes reproduce their kind, in Vorticella the gametes 

 are dissimilar, the conjugation permanent and complete, and 

 the resulting zygote is the sole reproductive individual. We 

 cannot hesitate to ascribe to the active microgamete the role 

 of the male, to the passive macrogamete the role of the female. 



