36 



CHAPTEE IV. 



WOKMS. 



PijAtthblminthbs or Flat-Worms. 



'Worms are most variable in form, habits, and structure. The}- 

 are of great interest, owing to their often complex life-historie.s. 

 To man and his animals they are often deadly enemies, giving 

 rise to such serious and often fatal diseases as Filariasis, 

 Trichimifiw, Miner's Disease, Strongylosis, and Twniosis. Xearly 

 every animal harbours one or more vermiceous guests. Some 

 seem to occasion little or no inconvenience to their host, whilst 

 others, if not fatal, are most annoying. Some live as parasites 

 in the blood (Htvmato::oa), others in the alimentary canal 

 (Tapeworms), others in the liver (Flukes), and even in the eye 

 (Filaria oculis). There are also worms, such as the earth- 

 worms, that are of the greatest service to man, helping to 

 fertilise the soil. Worms may be found in a great variety of 

 places. Largo numbers are marine ; others live in fresh water ; 

 yet others upon land, in damp earth, moss, and in excreta. It is, 

 however, those that lead a parasitic existence, living in some 

 other animal or plant, that we shall have to consider most fully. 

 Worms are bilateral animals with unsegmented or segmented 

 bodies. They never possess any jointed lateral appendages, 

 such as we shall see in the group (AnfhrnpoiJa) that includes 

 the insects and spiders. A dermal muscular system is de- 

 veloped, and there are present paired excretory tubes or canals. 



