84 



ANATOMY OF ANNELIDANS. 



d 



rd 



V TV 



Fig. 73. SECTION OF AN ANNELIDAN. 



ganglia; there is a pair of ganglia in each ring, which circum- 

 stance may account for the curious fact, that when, in some 

 instances, a part of a worm is cut off, both parts still live. 



4. Most anne'lidans have, at the anterior extremity of the body, 

 black spots which appear to be eyes of a very simple structure : 

 they never possess distinct organs of smell or of hearing ; but 

 they often bear on the head, or on each side of the neck, fila- 

 ments called antennse and tentacles, which seem to serve them 

 as organs of touch. In general these animals move by crawling, 

 and assist themselves in progression by the setce with which they 

 are armed, but they are never swift : many live buried in the 

 earth, or are enclosed in solid tubes which they never leave. 

 Most of them inhabit the sea. 



5. The digestive apparatus of anne'lidans is not particularly 

 remarkable, except for the sucker (?", j^. 74) with which the mouth 

 in many of them is furnished ; some have a long projectile trunk, 

 and they are often provided with small horny jaws. They all 

 appear to be carni'vorous. 



6. The blood of anne'lidans differs from that of all other inver- 

 tebrate animals by its red colour ; it circulates in a complete sys- 

 tem of arteries and veins, and often, it appears to be set in motion 

 by several fleshy ventricles which may be regarded as hearts 

 (Jig. 74, c). 



7. Almost all these animals live in water; they breathe by the 

 skin, or through branchia? (br), which resemble little packets of 

 fringe, attached along each side of the back. 



4. In what organs of sense are anne'lidans deficient ? 



5. What is the character of the digestive apparatus ? 



6. What is the peculiarity of the blood in anne'lidans ? 



7. How do anne'lidans breathe ? 



