THE LIFE OF THE SLIGHTLY COMPLEX ANIMALS 27 



colony, the two cells conjugate (Fig. 14) that is, fuse to 

 form a single cell. This new cell formed by the fusion of 

 two, develops a tough enveloping membrane of cellulose 

 and passes into what is called 

 the "resting stage." That is, 

 the cell remains dormant for a 

 shorter or longer time. It may 

 thus tide over a drought or a 

 winter. It may become dry or 

 be frozen, yet when suitable 

 conditions of moisture or tem- 

 perature are again present the 

 outer wall breaks and the pro- 

 toplasm issues as a large free- 

 swimming cell, which soon di- 

 vides into sixteen daughter 

 cells which constitute a new 

 colony. 



16. Eudorina. Another colo- 

 nial protozoan which much re- 

 sembles Pandorina^ but differs 

 from it in one interesting and 

 suggestive thing, is Eudorina. 

 In Eudorina elegans (Fig. 15) 

 the colony is spherical and is 

 composed of sixteen or thirty- 

 two cells. Each of these cells 

 can become the parent of a new 

 colony by simple repeated divi- 

 sion. But this simple mode of 

 reproduction, just as with Pan- 

 dorina, can not persist indefi- 

 nitely. There must be conjuga- 

 tion. But the process of mul- 

 tiplication, which includes conjugation, is different from 

 that process in Pandorina, in that in Eudorina the conju- 



B 



FIG. 14. Pandorina morum (after 

 GOEBEL). Three stages in the 

 conjugation and formation of the 

 resting spore. A, two cells just 

 fused; B, the two cells completely 

 fused, but with flagella still per- 

 sisting ; C, the resting spore. 



