CONCJLUSION. 189 



have before observed, but merely a fecundating 

 apparatus endowed with locomotion; and many 

 similar illustrations might be given. 



The preceding remarks may facilitate a consider- 

 ation of the zoological position of the minute 

 beings which have been the subjects of our con- 

 templation, and it will not excite surprise that 

 there should be a disposition to regard the Infusoria, 

 or many of them, as rudimentary forms of higher 

 organisms. Be this as it may, they furnish us 

 with the earliest and simplest exhibition of struc- 

 tures and capacities that we subsequently meet with 

 in a completer state. 



We want much more information as to the cycle 

 of changes which they are able to undergo, and the 

 precise conditions under which such changes take 

 place, before we can have an adequate conception 

 of the position in which they stand in relation to 

 the great system of animated nature, and the mode 

 in which they connect the organic and inorganic 

 worlds. 



The members of the highest class described in 

 the preceding pages, the Polyzoa, belong to the 

 sub-kingdom of Mollusca, and in that division of 

 animated nature the nervous system varies very 

 much in degree of development. The lowest forms 

 possess a single ganglion, such as we observed in 

 the Plumatella; additional ganglia are added as 



