84 ANNELIDA. 



FIRST CLASS OF ARTICULATED ANIMALS. 



ANNEL IDA WORMS. 



THE body of the Annelidans is composed of a succes- 

 sion of numerous rings, all of which are merely 

 repetitions of each other. The first segment, although 

 it differs but little from the rest, 

 is called the head. The skin is 

 generally soft, and the rings 

 never horny or stony. Many 

 Annelidans are entirely destitute 

 of legs, as, for example, the leech 

 (Fig. 53) ; and when these organs 

 exist they are never formed of 

 pieces jointed together end to 

 end, as they are in insects, lob- 

 sters, or spiders ; they are merely 



FIG. 58. FOOT OF NAIS. n 1 ^1 %l V 



nesny protuberances that support 

 bunches of stiff setas, or bristles, and are used as oars 

 to row the animal through the water. (Fig. 58.) 



Most Annelidans at the anterior extremity of their 

 body are furnished with black spots, which appear 

 to be eyes of very simple structure : they often 

 have on the head, or on the sides of the neck, fleshy 

 filaments called tentacles, which are not only delicate 

 instruments of touch, but sometimes perform other 

 important functions, as we shall see hereafter. In 

 general these animals can crawl upon the ground by 

 means of their setae ; many live buried in the earth, 

 or are enclosed in tubes which they never leave ; 

 they mostly inhabit the sea, and are, with one or 

 two exceptions, carnivorous. 



The Annelidans are divided by zoologists into 

 three orders, according to the nature and disposition 

 of their respiratory apparatus. Some appear to 



