CHAPTER XIII 



THE WORM-LIKE ANIMALS Subkingdom VERMES 



ALTHOUGH it is convenient to -have a single group in which to include the vari- 

 ous 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 subkingdoms. 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 characteristics, 

 distinctive of any of the other groups. 



BRISTLE; WORMS OR ANNELIDS Class Annelida 



The more highly organized members of this group show unmistakable points of 

 affinity with the arthropods, such as Apus among the Crustacea, and Peripatns, 

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

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



from the arthropods. In the 

 worms the jaws, when pres- 

 ent, are not modified append- 

 ages, but are merely horny 

 skeletal pieces developed 

 from the walls of the front 

 end of the alimentary canal; 

 the appendages, when pres- 

 ent, are not segmented, but 

 merely unjointed processes 

 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 chsetopods 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 the segments 

 (3404) 



GROUP OF BRISTLES OF AN ANNEUD (enlarged 100 times). 



