VIII NE MA TO DA 97 



but seems to be a special organ of touch and perhaps also a 

 weapon, since in some cases it carries a sharp spine, though 

 not in the genus lAneus mentioned below. The alimentary 

 canal, unlike that of Turbellaria, ends in an anus. 



A well-known marine member of this class is the curious 

 Linens marinus, the Sea Longworm or Sea Snake, which, it is 

 said, may even grow to a length of 1 00 feet. It is, perhaps, 

 the longest animal known. 



Lineus is found in rock-pools near low tide mark ; its body 

 is about as thick as a boot-lace, and it twists it in and out into 

 complicated knots (Fig. 50). In spite of its ability to twist 

 in this way, the body is very brittle, and it is therefore diffi- 

 cult to handle without injuring it, though if successfully 

 transferred to a sea-water tank it will thrive, and its velvety- 

 looking body, with changing purplish hues, will be a beautiful 

 object. The front end of the body is blunt. Sometimes 

 there may be seen protruding from it a long fine thread ; 

 this is the characteristic proboscis with which it is said to 

 lasso its victims— chiefly marine worms — drawing them to 

 its mouth, and swallowing them whole. 



PHYLUM VII. : NEMATODA, THE EOUND OR 

 THREAD-WORMS 



These "worms" have a long, thin, unsegmented body, 

 round in section, and with a muscular body -wall, thicker 

 than that in Flatworms. 



A body-cavity is present, and this too marks them off from 

 Flatworms, which have no body-cavity. They are usually small 

 forms, though some reach the length of 5 or 6 feet. They 

 move with a wriggling motion. Most of them are parasitic. 



Ascaris lumh-icoides is a common roundworm, parasitic in 

 the intestine of man; it may be nearly 16 inches long. 



Trichina spiralis is another parasite, at first living in the 

 intestine of man, and then in his muscles, causing the disease 

 known as " trichiniasis." In another phase of its life-history it 

 is parasitic in pig, producing what is known as " measly " pork. 



Many other Nematods attack valuable domesticated 

 animals, so that on the whole they are a class distinctly 

 hostile to the welfare of man. 



Some, however, are non-parasitic, living in damp earth or 

 VOL. I H 



