190 ANIMALS AND PLANTS vi 



characteristically a plant. Under ordinary cir- 

 cumstances, the Chlamydomonas multiplies by 

 simple fission, each splitting into two or into four 

 parts, which separate and become independent 

 organisms. Sometimes, however, the Chlamy- 

 domonas divides into eight parts, each of which is 

 provided with four instead of two cilia. These 

 "zoospores" conjugate in pairs, and give rise to 

 quiescent bodies, which multiply by division, and 

 eventually pass into the active state. 



Thus, so far as outward form and the general 

 character of the cycle of modifications, through 

 which the organism passes in the course of its 

 life, are concerned, the resemblance between 

 Chlamydomonas and Hcteromita is of the closest 

 description. And on the face of the matter there 

 is no ground for refusing to admit that Heteromita 

 may be related to Chlamydomonas, as the colourless 

 fungus is to the green alga. Volvox may be com- 

 pared to a hollow sphere, the wall of which is 

 made up of coherent Chlamydomonads ; and which 

 progresses with a rotating motion effected by the 

 paddling of the multitudinous pairs of cilia which 

 project from its surface. Each FWmi'-monad, 

 moreover, possesses a red pigment spot, like the 

 simplest form of eye known among animals. The 

 methods of fissive multiplication and of conjugation 

 observed in the monads of this locomotive globe 

 are essentially similar to those observed in Chlamy- 

 domonas ; and, though a hard battle has been 



