146 ZOOLOGY 



184. Phylum Annulata (Segmented Worms: with rings). 

 This phylum is similar to the arthropods in that the body is 

 bilaterally symmetrical, is segmented, and has paired append- 

 ages to many of the segments. It differs from them in the 

 fact that the appendages, when present, are not jointed but 

 are merely setae or hairs in sockets or on fleshy prominences. 

 The segments are more nearly homonomous than in typical 

 arthropods. The earthworm, many types of aquatic worms, 

 and leeches are included here. 



185. Unsegmented Worms (embracing numerous ill-as- 

 sorted animals of doubtful relationship). Here may be in- 

 cluded a number of small groups many of which have long 

 been grouped with the Annulata and called "worms." They 

 are not sufficiently alike to be regarded as one distinct phylum; 

 Indeed there are probably three or four small phyla included. 

 The majority of them are bilaterally symmetrical, unSegmented 

 and without appendages. They differ from the mollusks in 

 that they do not possess a mantle and do not secrete a shell. 

 Many of them are parasitic. Among these animals of doubtful 

 relationship may be included the "flat- worms," "thread- worms," 

 the nemertea, rotifers, and others. 



1 86. Ccelomata (with ccdom) and Ccelenterata (hollow 

 inside). All the animals thus far considered possess during 

 some stage of life a more or less developed body cavity or 

 ccelom (see 58) distinct from the digestive tract. For this 

 reason they are sometimes known collectively as Ccelomata. 

 All the remaining many- celled animals have a general cavity 

 which serves both as a body cavity and a digestive tract (gastro- 

 vascular cavity), or to speak more exactly, there is no true 

 body cavity. Of these the phylum Ccelenterata is the chief 

 illustration. Here belong the jelly-fish, sea-anemone, corals. 

 They are all aquatic and are more or less tubular, sac-shaped 

 animals often attached by one end, with the mouth, which also 

 functions as the anus, at the other surrounded by clusters of 

 tentacles. Many secrete skeletons, and some form immense 

 attached colonies. 



