38 INVERTEBRATE MORPHOLOGY. 



nucleus. The conjugation micronucleus, formed by tlie fusion 

 of the male and female pronuclei, divides twice, forming four 

 microuuclei, and this is followed by a fission of the entire 

 Infusorian, each of the daughter forms so produced possessing 

 two micronuclei. One of these, enlarging, becomes the new 

 nucleus, while the other remains as the micronucleus. This 

 complicated process may perhaps be better followed in the 

 accompanying diagram (Fig. 19). 



O 



Fig. 19. — Diagkam to Illustrate the Bbhayiob op the Ntjclei and 

 Micronuclei during Conjugation in Infusoria (after Maupas). 



In the majority of forms the conjugation is a temporary 

 process, the two individuals separating after the exchange of 

 pronuclei. In Vorticella, however, a permanent fusion occurs. 

 By repeated longitudinal fission a Vorticella becomes divided" 

 into a number of small individuals which leave their stalks 

 and swim about freely in the water. Should one of them 

 come into contact with a large individual a complete and 

 permanent fusion of the small with the large one occurs. 



SUBKINGDOM PROTOZOA. 

 I. Class Khizopoda. — Protozoa with lobe-like or filamentous pseudopodia. 

 1. Order Foraminifera. — Pseudopodia without axial support; shell 

 when present horny or calcareous. 

 (a) Shell absent. Ama'ba. 

 (6) Shell horny. Arcella, Euglypha. 



(c) Shell of foreign particles cemented together. Bifflugia. 



(d) Shell calcareous, imperforate. Qromia. 



(e) Shell calcareous, perforate. Miliola, Ifodosaria, Textu- 



laria, Globigerina, Rotiila, Acermdaria. 



