650 THE POPULAR SCIENCE MONTHLY. 



one, as I have said, very closely resembles Ileteromita lens in every 

 particular, except that it lias a separately distinguishable central par- 

 ticle or " nucleus," which is not certainly to be made out in Iletero- 

 mita lens ; and that nothing is said by Messrs. Dallinger and Drysdale 

 of the existence of a contractile vacuole in this monad, thougb they 

 describe it in another. 



Their Ileteromita, however, multiplied rapidly by fission. Some- 

 times a transverse constriction appeared ; the hinder half developed a 

 new cilium, and the hinder cilium gradually split from its base to its 

 free end, until it was divided into two; a process which, considering 

 the fact that this fine filament cannot be much more than xroVoT *^^ ^^ 

 inch in diameter, is wonderful enough. The constriction of the body 

 extended inward until the two portions were imited by a narrow istli- 

 mus ; finally they separated, and each swam away by itself, a com- 

 plete Ileteromita, provided with its two cilia. Sometimes the con- 

 striction took a longitudinal direction, with the same ultimate result. 

 In each case the process occupied not more than six or seven minutes. 

 At this rate, a single Ileteromita would give rise to a thousand like 

 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 liours ; or, if we give edich Ileteromita 

 an hour's enjoyment of individual existence, the same result will be 

 obtained in about a day. The apparent suddenness of the appearance 

 of multitudes of such organisms as these, in any nutritive fluid to 

 which one obtains access, is thus easily explained. 



During these processes of multiplication by fission, the Ileteromita 

 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 Ileteromita. 



A still more remarkable phenomenon is that kind of multiplica- 

 tion which is preceded by the union of two monads, by a process 

 which is termed conjugation. Two active Heteromitoe become applied 

 to one anothei', and then slowly and gradually coalesce into one body. 

 The two nuclei run into one ; and the mass resulting from the conju- 

 siation of the two Heteromitce. th\is fused tooether, 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 visi- 

 ble traces of organization have disappeared, falls into a state of rest. 

 Sudden wave-like movements of its substance next occur; and, in a 

 short time, the apices of the triangular mass burst, and give exit to a 

 dense yellowish, glairy fluid filled with minute granules. Tliis pro- 

 cess, which, it will be observed, involves the actual confluence and 

 mixture of the substance of two distinct organisms, is eflfected in the 

 space of about two hours. 



