34 



THE INVERTEBRATA 



organisms in general. Most of these researches have been carried out 

 upon ciliata. They have led to two theories: (i) that syngamy effects 

 a periodical rejuvenescence of the organism ; (2) that it produces new 



Fig. 26. Conjugation of ciliates. A, Paramecium. B, Vorticella. Both at the 

 moment of the exchange of male pronuclei, meg. fragments of disintegrating 

 meganuclei ; mi. micronuclei : in each the male and female pronuclei produced 

 by the division of a single nucleus still hang together by their spindle, but are 

 parting, the male to pass into the other conjugant, the female to remain behind ; 

 mi.' abortive division products of the original micronucleus. 



Fig. 27. A diagram of the behaviour of the micronuclei during the conjuga- 

 tion of Paramecium caudatum. From Borradaile. The white circles represent 

 the portions which degenerate. 



types of individual and therefore gives the species more chances of 

 survival in the struggle for existence. 



(i) Cultures of protozoa in which conjugation is prevented are 

 liable after a time to fall into an unhealthy condition known as de- 



