HIRUDINEA 69 



The nereis, or sand-worm, which is found on the seashore, has a distinct 

 head, bearing eyes and tactile sense organs, such as tentacles and palpi. 

 Each segment has a fleshy outgrowth, the parapodium, bearing many bristles. 

 " This is the first appearance of true appendages, though they are not 

 jointed to the body nor in themselves." 



The sand-worm varies in color in different stages, and the length varies 

 from 6 inches to 2 feet. 



It has an eyersible pharynx, which, when infolded, conceals two horny 

 jaws. These jaws are deeply notched and the ends are incurved. When 

 food is taken the pharynx is everted, the jaws thrust forth, and the prey 

 seized and swallowed. 



CLASS H. GEPHYR'EA 



Class Gephyr'ea is composed of oval or spindle-shaped worms, 

 which are unsegmented in the adult form. Setae are entirely 

 wanting. The mouth, which is at the anterior end, is either 

 surrounded by tentacles or overhung by a " proboscis " which 

 may be several times the length of the body. 



These worms are widely distributed. They live in both 

 deep and shallow water and, " for the most part, either in 

 natural rock-fissures or in burrows which they excavate in sand 

 or mud or in coral or rock." 



CLASS m. HIRUDIN'EA 



The body of the leech tapers at both ends and is flattened 

 dorsoventrally. It is composed of many segments which are 

 superficially divided into several rings, so that there are not so 

 many true segments as there are surface rings. 



The principal order of this class contains the common fresh- 

 water leech familiar to barefoot boys. It is a temporary para- 

 site on vertebrates. 



The leech (Fig. 51) has no setae nor appendages, but is pro- 

 vided with two suckers. The one on the posterior ventral sur- 

 face is used for attachment in locomotion, and the other, which 

 surrounds the mouth and is not well developed, is used in suck- 

 ing the blood into the large crop. In the pouches of this crop, 

 it is said, enough blood can be stored to last a year. A narrow 

 stomach and a short intestine follow the pouched crop. The 

 ccelom is considerably obliterated by a growth of muscle and 

 connective tissue, called parenchyma. 



Leeches are hermaphroditic. The eggs are usually laid 

 in small packets or cocoons, and these are deposited in moist 



