Sexual Diversity in Protozoa 123 



Vorticella produces just before the fertilizing process two 

 half nuclei, as Paramecium does, but in the large "female" 

 one is absorbed and disappears, while in the small "male" 

 likewise one is absorbed and disappears. The remaining 

 half nucleus of the "male" then passes into the "female," 

 and unites with its remaining half nucleus. (See the dia- 

 gram of the process in comparison with that in Paramecium, 

 in Figure 35). 



Figure 36. Mating in the mould, Mucor, after De Bary. A to E, 

 successive stages. The large black body at E formed by the union of 

 the ends of the two branches, is the zygospore, which later separates 

 off, and produces a new plant. 



In Paramecium, it was held by Cull (1907) that there is a 

 less advanced stage of a similar process ; though the two in- 

 dividuals look and act alike, they still are different, since 

 after mating one reproduces more vigorously than the other. 



Cases are known in which the individuals of a species are 

 really physiologically diverse as to sex, although in appear- 

 ance they are alike. This has been worked out fully by 

 Blakeslee (1904) in the common moulds, Mucor. Here the 



