40 THOUGHTS ON ANIMALCULES. 



the other monads, but it presents an extraordinary 

 peculiarity. Jf we look attentively at the large Yolvox 

 now slowly revolving through the water, bristling with 

 long filaments, which are the protruded horns of the 

 monads, (pi. n, fig. 10), we may discern within the 

 globe several lesser ones, apparently differing from the 

 outer globe only in size: these are new generations 

 ready to escape, and go through the same changes as 

 the parent group. These internal globes of young Yol- 

 voces are produced, in consequence of the spontaneous 

 division in this species of monad, taking place only from 

 the inside of the globular envelope. New spherical 

 groups are thus thrown off into the cavity of the parent 

 carapace, where they remain till they attain a certain 

 stage of development. Some part of the integument of 

 the outer globe then gives way, (see pi. u, fig. 9), and the 

 young ones escape, and commence their independent 

 existence. The internal globes are generally six or eight 

 in number, but occasionally as many as twenty occur ; 

 they are green, have an entire margin, and may some- 

 times be seen to move while within the primary globe. 

 There are apertures by which the water has free access 

 to the interior of the whole series. The revolving mo- 

 tion of the Yolvox, by which it is propelled through the 

 water, is effected by the incessant action of the vibratile 

 cilia, and is automatic, (that is, an organic or involuntary 



