174 ANIMALS AND PLANTS. [LECT. 



microscopic green bodies, each of which consists of a 

 protoplasmic central substance invested by a struc- 

 tureless sac. The latter contains cellulose, as in ordi- 

 nary plants ; and the chlorophyll which gives the green 

 colour enables the Chlamydomonas to decompose car- 

 bonic acid and fix carbon as they do. Two long cilia 

 protrude through the cell-wall, and effect the rapid 

 locomotion of this "monad," which, in all respects 

 except its mobility, is characteristically a plant. 

 Under ordinary circumstances, the Chlamydomonas 

 multiplies by simple fission, each splitting into two or 

 into four parts, which separate and become independent 

 organisms. Sometimes, however, the Chlamydomonas 

 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 con- 

 cerned, the resemblance between Chlamydomonas and 

 Heteromita 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 Chlamydo- 

 monas, as the colourless fungus is to the green alga. 

 Volvox may be compared to a hollow sphere, the 

 wall of which is made up of coherent Chlamydo- 

 monads ; and which progresses with a rotating motion 

 effected by the paddling of the multitudinous pairs of 

 cilia which project from its surface. Each Volvox- 



