92 PROTOZOA. 



of a micro-nucleus. These fragments are each one-fourth 

 part of the original overgrown micro-nucleus. 



(2) In each individual one of the parts moves across 

 into the other individual and fuses with the remaining part 

 of that individual. Sometimes the migrating parts are 

 termed the male pronuclei ^ and the other two the female 

 pronuclei, 



(3) Soon after this communication between the two 

 individuals becomes interrupted and they part. In the 

 meanwhile the single-fused nucleus in each divides into two 

 and then into four, so that each individual has then four 

 nuclei. 



(4) Two quarters pass to each end of the animal and 

 binary fission takes place. One quarter grows into a macro- 

 nucleus and the other remains a micro-nucleus. The result 

 is a pair of offspring with a macro nucleus and a micro- 

 nucleus each 



This account should be carefully compared with the 

 remarks in Chapter V. It will then be seen that the 

 presence of two kinds of nuclei is the principal factor 

 causing complication. 



Paramoiciuin is a type of the Sub-kingdom PROTOZOA, 

 for it is a single cell with all the vital activities confined 

 therein. It is a type of the phylum CORTICATA, for it 

 has a definite shape of the body due to a Hmiting cortex ; 

 this involves the important feature of a definite mouth. 

 In the CORTICATA it belongs to the class Ciliata for 

 its locomotive organs are in the form of cilia. The cilia 

 are evenly distributed over the surface of the body, and 

 hence it is a member of the order Holotricha. 



III.— VORTICELLA. 



Vorticella is a small freshwater and marine animal closely allied to 

 the last type, from which it chiefly differs in being sedentary or fixed. 

 It may affix itself to almost any foreign body, living or non-living. The 

 body of the animal is bell-shaped with a long stalk. As in Paraniacitmi 

 there is a cuticle and cortex. The cilia are confined to ihe rim of 

 the bell and produce vortex-currents by which food-particles are 

 brought to the mouth. The thickened ciliated rim is called the peri- 

 stome., and immediately inside there runs a circular groove leading 

 down at one part into a funnel-shaped vestibtile. The base of the 



