214 ZOOLOGY 



of its host. In the case of pork, if the meat is eaten in an un- 

 cooked condition, the cyst is dissolved off by the action of the 

 digestive fluids, and the living trichina becomes free in the intestine 

 of man. Here it bores its way through the intestine walls and 

 enters the muscles, causing inflammation there. This causes a 

 painful disease known as trichinosis. 



Some roundworm parasites live in the skin, and others live in 

 the intestines of the horse. Still others are parasitic in fish and 

 insects, one of the commonest being the hair snake, often seen in 

 country brooks. 



Classification of Segmented Worms (Anntjlata) 



Class I. Chcetopoda (bristle-footed). Segmented worms having setse. 



Subclass I. Polychceta (many bristles). Having parapodia and usually head 



and gills. Example, sandworm. 

 Subclass II. Oligochceta (few bristles). No parapodia, head, or gills. Ex- 

 ample, earthworm. 

 Class II. Discophora (bearing suckers). No bristles, two sucking disks present. 

 Example, leech. 



Platyhelminthes (Flatworms) 



Body flattened in dorso- ventral direction. 



Class I. Turbellaria. Small aquatic, mostly not parasitic. Example, planarian 

 worm. 



Class II. Trematoda. Usually parasitic worms which have complicated life 

 history. Example, liver fluke of sheep. 



Class HI. Cestoda. Internal parasites ha^'ing two hosts. Example, tape- 

 worm. 



Nemathelminthes (Roundworms) 



Threadlike worms, mostly parasitic. Examples, vinegar eel and 

 Trichina. 



Reference Books 



for the pupil 



Davison, Practical Zoology, pages 150-161. American Book Company. 

 Herrick, Text-book in General Zoology, Chap. TX. American Book Company. 

 Jordan, Kellogg, and Heath, Animal Studies, VI. D. Appleton and Company. 



FOR THE teacher 



Darwin, Earthworms and Vegetable Mould. D. Appleton and Company. 

 Sedgwick and Wilson, General Biology. Henry Holt and Company. 



