166 ANIMALS AND PLANTS. [LECT. 



Of the four monads described and figured by these 

 investigators, one, as I have said, very closely 

 resembles Heteromita lens in every particular, except 

 that it has a separately distinguishable central particle 

 or " nucleus," which is not certainly to be made out 

 in Heteromita lens; and that nothing is said by 

 Messrs. Dallinger and Drysdale of the existence of a 

 contractile vacuole in this monad, though they 

 describe it in another. 



Their Heteromita, however, multiplied rapidly by 

 fission. Sometimes a transverse constriction ap- 

 peared ; 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 xrmTJcJt) f an i ncn * n 

 diameter, is wonderful enough. The constriction of 

 the body extended inwards until the two portions 

 were united by a narrow isthmus ; finally, they separ- 

 ated and each swam away by itself, a complete Heter- 

 omita, provided with its two cilia. Sometimes the 

 constriction took a longitudinal direction, with the 

 same ultimate result. In each case the process occu- 

 pied not more than six or seven minutes. At this 

 rate, a single Heteromita 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 hours ; or, if we give each 

 Heteromita an hour's enjoyment of individual exist- 

 ence, the same result will be obtained in about a day. 



