158 INSECTS INTESTINAL WORMS DIAGRAM 6. 



and are called suckers. The first segments behind the head are 

 still smaller than this ; but they become larger and larger, and 

 the last are nearly half an inch broad by as much long. There 

 are sometimes a large number of these rings ; there may be 

 several hundreds of them, and the entire worm generally measures 

 several yards. All the rings grow behind the head one after the 

 other, so that the last is always the oldest. The head continues 

 to produce fresh ones as long as it lives. For this reason when a 

 piece of the tape-worm has been voided, it is necessary to look if 

 the head is there ; for if the head has remained in the body, it 

 will form new segments, and at the end of some time will re- 

 produce a worm as long as the piece discharged. 



Isolated segments of a tsenia detached from the extremity of the 

 animal are sometimes discharged. The presence of one or more 

 taenias in the intestines may affect the health ; but it is a mistake 

 to suppose that it eats part of the food which is taken. The tsenia 

 has not even a mouth with which it could swallow anything. 



The Flukes. Flat parasitic worms which crawl like slugs are 

 often found in the liver of sheep ; some are very small, and only 

 a quarter of an inch long, and others measure an inch or an inch 

 and a-half in length, and resemble a leaf; they are called flukes. 

 We also meet with small black or grey worms, very similar 

 to flukes, in marshes, which crawl rapidly on aquatic plants or 

 on the surface of the vessel in which they are placed. These 

 animals are called planarise, and are remarkable, because if they 

 are longitudinally divided in two, as far as the middle of the body, 

 with a sharp pair of scissors or a razor, each half completes itself, 

 and the animal has soon two heads or tails, according as it has 

 been divided in front or behind ; and if we then finish dividing 

 it, we have two complete and separate animals instead of one. 



Worm of tJie Staggers. Parasitic worms do not live only in the 

 intestines. We have just seen that the flukes are found in the 

 liver ; others are found in the brain. Sometimes sheep are 

 attacked by a disease well known to shepherds, and which causes 

 them to turn round instead of walking straight. This complaint 



