174 ANIMALS AND PLANTS. 



itself in the course of an hour, to about a million in 

 two hours, and to a number greater than the generally 

 assumed number of human beings now living in the 

 world in three hours; or, if we give each Heteromita 

 an hour's enjoymsnt of individual existence, the same 

 result will be obtained in about a day. The apparent 

 suddenness of the appearance of multitudes of such or- 

 ganisms as these, in any nutritive fluid to which one 

 obtains access, is thus easily explained. 



During these processes of multiplication by fission, 

 the Heteromita remains active; but sometimes another 

 mode of fission occurs. The body becomes rounded and 

 quiescent, or nearly so ; and, while in this resting state, 

 divides into two portions, each of which is rapidly con- 

 verted into an active Heteromita. 



A still more remarkable phenomenon is that kind of 

 multiplication which is preceded by the union of two 

 monads, by a process which is termed conjugation. Two 

 active Heteromitce become applied to one another, and 

 then slowly and gradually coalesce into one body. The 

 two nuclei run into one; and the mass resulting from 

 the conjugation of the two Heteromitce^ thus fused to- 

 gether, has a triangular form. The two pairs of cilia are 

 to be seen, for some time, at two of the angles, which 

 answer to the small ends of the conjoined monads ; but 

 they ultimately vanish, and the twin organism, in which 

 all visible traces of organisation have disappeared, falls 

 into a state of rest. Sudden wave-like movements of its 

 substance next occur; and, in a short time, the apices 



