OTHER UNSEGMENTED WORMS 



187 



no coelom. The nervous system consists of two ganglia, one on each 

 side of the proboscis at the anterior end of the body connected by com- 

 missures dorsal and ventral to the proboscis, and two nerve trunks run- 

 ning backward along the sides of the body. Many of them have eyespots, 

 and some possess eyes with a sort of lens, pigment, and retina. 



A few species are found in moist earth and fresh water, but most 

 of them are marine, being found coiled up under stones and other objects 

 on the beach at low tide or crawling over the sand as the water recedes 

 with the falling of the tide. Many nemertines are brightly colored. 

 They are exceedingly soft-bodied and when lifted have not sufficient 



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Mese/^chyme 

 ce// 



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 /obe 



Fig. t)7. — The pilidium larva. Median section, showing the inner surface of the 

 ventrolateral lobe on the farther side. This lobe is hollow, containing a prolongation of the 

 cleavage cavity. {Compiled from several sources.) 



consistency to support their own weight. As one raises them by one 

 end they continue to stretch until finally they may even break in two. 

 One genus, Malacohdella, is parasitic in a European marine bivalve 

 mollusk. 



The bandworms feed on other animals, both dead and living. They 

 move by means of cilia which cover the surface of the body, by constric- 

 tions of the body wall, by vertical undulations of the body, or by using 

 the proboscis as an organ of attachment. They secrete a great deal of 

 mucus which may of itself become firm and produce a protective tube, 

 or they may make a tube by sticking together particles of sand. They 

 possess great powers of regeneration, which might be expected consider- 

 ing the readiness with which the body is broken. They also show autot- 

 omy, which is the abihty of an animal itself to break its body into 

 pieces. 



The larval nemertine, known as a pilidium, is a ciliated swimming 

 larva, somewhat conical in form, with downwardly projecting lateral 

 lobes and a long tuft of cilia at the apex (Fig. 97). 



