168 MARINE INVERTEBRATES 



lar covering; others remain naked. All are covered with vibrat- 

 ing cilia, which is a universal feature of flatworms. In color 

 they may be white, yellow, green, red, purple, etc., and some- 

 times they are banded or striped with a contrasting color. The 

 ventral is usually lighter than the dorsal surface. 



The principal characteristic of the nemertean worms is a long 

 thread-like organ, known as the proboscis. This lies in a sheath 

 along the center of the dorsal surface, and is quickly thrown 

 out to a great length, and as quickly completely withdrawn within 

 the body. The proboscis is slender, hollow, muscular, and full 

 of nerves. It reaches the outside through a pore at the ante- 

 rior end of the body, and has no connection with the alimen- 

 tary system. It is used as a feeler and as a weapon. Some 

 species have a sharp spine at the end of the proboscis, others 

 have stinging-cells. The proboscis is sometimes so forcibly 

 ejected that it breaks off, in which case it retains its vitality for 

 some time, and seems as if it were itself a worm. A new pro- 

 boscis is quickly grown by the worm to take the place of a lost 

 one. The head is a little broader than the body, and has eyes 

 arranged in one or several pairs on each side. The mouth is on 

 the ventral surface, near the anterior end, has thick lips, and is 

 very dilatable. Through the mouth the animal ejects a part of 

 the esophagus and envelops its prey, which is often of consider- 

 able size. Cha3topod worms they often swallow whole ; the soft 

 parts, after being digested, are carried off through the regular 

 passages, ending in the ciliary flames (page 164), while the indi- 

 gestible parts are ejected at the anus. Often the spines and 

 bristles find their way out by perforating the intestine and the 

 body-wall, without apparently doing the worm any injury. The 

 perforated parts quickly heal. 



These worms have the strange power of regenerating lost parts ; 

 mutilated portions are soon repaired. The anterior end, when 

 severed from the rest of the body, grows again into a complete 

 individual, while the posterior end continues to perform part of 

 its functions and retains its vitality for a considerable time be- 

 fore dying. One species, Linens sangiiineus, is capable, after being 

 broken in pieces, of regenerating each section into a perfect worm. 



