VII.] ANIMALS AND PLANTS. 173 



which are divided into cells. Its greenness is due to 

 its chlorophyll, and it undoubtedly has the manufac- 

 turing power in full degree, decomposing carbonic 

 acid and setting oxygen free, under the influence of 

 sunlight. But the protoplasmic contents of some of the 

 cells of which the plant is made up occasionally divide, 

 by a method similar to that which effects the division 

 of the contents of the Peronospora spore; and the 

 severed portions are then set free as active monad-like 

 zoospores. Each is oval and is provided at one 

 extremity with two long active cilia. Propelled by 

 these, it swims about for a longer or shorter time, but 

 at length comes to a state of rest and gradually grows 

 into a Coleochcete. Moreover, as in the Peronospora, 

 conjugation may take place and result in an oospore ; 

 the contents of which divide and are set free as 

 monadiform germs. 



If the whole history of the zoospores of Perono- 

 spora and of Coleochcete were unknown, they would 

 undoubtedly be classed among " Monads " with the 

 same right as Heteromita ; why then may not 

 Heteromita be a plant, even though the cycle of 

 forms through which it passes shows no terms quite 

 so complex as those which occur in Peronospora and 

 Coleochcete ? And, in fact, there are some green 

 organisms, in every respect characteristically plants, 

 such as Chlamydomonas, and the common Volvox, or 

 so-called " Globe animalcule," which run through a 

 cycle of forms of just the same simple character as 

 those of Heteromita. 



The name of Chlamydomonas is applied to certain 



