REPRODUCTION 523 



meet with frequent examples of this process of 

 Jissiparous oeuenifiou, as it is termed, among the 

 infiisory animalcules. Many species of Monads, 

 for instance, which are naturally of a globular 

 shape, exhibit at a certain period of their develope- 

 ment a slight circular groove round the middle of 

 their bodies, which by degrees becoming deeper, 

 changes their form to that of an hour-glass ; and 

 the middle part becoming still more contracted, 

 they present the appearance of two balls, united by 

 a mere point. The monads in this state are seen 

 swimming irregularly in the fluid, as if animated 

 by two different volitions; and, apparently for the 

 purpose of tearing asunder the last connecting 

 fibres, darting through the thickest of the crowd of 

 surrounding animalcules ; and the moment this 

 slender ligament is broken, each is seen moving 

 away from the other, and beginning its independent 

 existence. This mode of separation is illustrated 

 by Fig. 462, representing the successive changes 



■r^ C\ C^ O Q O 



462 o B y O © O 



463 



of form during its progress. In this animalcule the 

 division is transverse, but in others, for example in 

 the Vorticella (as shown in Fig. 403), and in most 

 of the larger species, the line of separation is longi- 

 tudinal. Some species of Monads, again, separate 

 themselves at once, by a crucial line of division 

 into four equal parts ; and the Gonium pecfo/ale, by 

 a double process of the same kind, divide them- 



