CHAPTER XIII. 



The Worm-Like Animals, — Subkingdom VERMES. 



Although it is convenient to have a single group in which to include the 

 various kinds of worm-like animals, it has been frequently pointed out that there 

 is no natural sanction for such an arrangement, and that it is highly probable they 

 ought to be divided into several subkingdoms. Accordingly, the present division 

 of the animal kingdom must be regarded as a convenient receptacle in which to 

 place such Invertebrates as cannot be readily assigned to any of the other sub- 

 kingdoms. This being so, it will be evident that it is only possible to describe this 

 assemblage of heterogeneous elements by stating that the various classes into 

 which it is divided resemble each other in the negative feature of not possessing 

 the characters distinctive of any of the other groups. 



Bristle- Worms, or Annelids, — Class Annelida. 



... ... 



The more highly organised members of this group show unmistakable points 

 of affinity with the arthropods, such as Apus amongst the Crustacea, and PeripatvM, 

 which approaches the Centipedes. It is possible, however, to mention certain 

 characters, which, so far as known, serve to distinguish the bristle-bearing worms 



from the arthropods. In 

 the worms the jaws, when 

 present, are not modified 

 appendages, but are merely 

 horny skeletal pieces devel- 

 oped from the walls of the 

 front end of the alimentary 

 canal ; the appendages, when 

 present, are not segmented, 

 but merely unjointed pro- 

 cesses of the sides of the 

 body, and certain parts of 

 the body are ciliated, or 

 beset with fine hair -like 

 threads, such threads being 

 seldom found at any stage in 

 the life-history of an arthropod. To distinguish the annelids or chgetopods from 

 the groups that follow, it may be said that there is usually a distinct prostomium, 

 or lobe in front of the mouth, that definitely arranged bristles are implanted in 



OHOtjp of bristles of an annelid (enlarged 100 times). 



