316 SOME COMMON INTERNAL PARASITES [CH. IX 



Ctenotcenia and Andrya. In none of these instances is 

 the life-history known and much remains to be done in 

 elucidating the mode of infection. 



A tapeworm can only be dislodged by resorting to 

 purgatives. The animal should be denied all food for a 

 day, and then areca nut or male fern administered. 

 Thymol is also a valuable remedy, but care should be 

 taken to avoid administering it in company with any 

 solvent such as oils (or, in the case of man, alcohol), lest 

 it should be absorbed into the system. 



Nematoda (Thread- or Round- Worms). 



The majority of these remarkably hard, unsegmented 

 worms are of minute, and often microscopic, size, but some 

 species attain a length of several feet. Their smooth 

 surface and finely tapering body enable them to insinuate 

 themselves into the tissues of animals and plants, and 

 account for their extraordinary prevalence. They are 

 more generally known by the diseases they produce in 

 animals and in plants than by their actual appearance. 

 In this country, of 'those parasitic in man, Ascaris lum- 

 bricoides, which occurs in the intestine more commonly 

 in children than in adults, is the best known. The eggs 

 develop in water or damp earth and liberate their 

 embryos when re-introduced into the human alimentary 

 canal. Another species of this genus, A. megalocephala, 

 occurs in horses and asses, and may sometimes be seen, 

 being a large worm about 10 inches in length, in the 

 droppings of these animals. The complete life-history of 

 this species is not known with certainty. 



