Internal Parasites 



135 



breaks are usually confined to comparatively small areas and 

 are perhaps more common in the southern states. 



Etiology. — The tape worms of poultry, like those which 

 infest man and the domestic 

 animals, are long, flat, segmented 

 worms (Fig. 19). The anterior 

 end of the animal possesses a 

 number of hooks or suckers by 

 which it attaches itself to the walls 

 of the intestine. Back of this 

 head the entire animal consists 

 of a long series of segments or 

 proglottids. The segments near- 

 est the head are the smallest and 

 it is at this region that new 

 segments are constantly being 

 formed. The farther from the 

 head they get the larger the seg- 

 ments become. Towards the pos- 

 terior end of the worm the seg- 

 ments develop sexual organs and 

 later become filled with eggs. 

 As soon as the eggs are fertilized 

 and mature the segment contain- 

 ing them drops off and passes 

 to the exterior with the feces of 

 the host. Each segment of this 

 kind contains thousands of eggs. 



If these eggs are to develop 

 farther they must be swallowed 

 by some intermediate host (as a 

 worm, snail or insect). The 

 egg then hatches into a 6-hooked embryo which bores its 

 wav from the intestine into the bodv cavity of the inter- 



FiG. 19. — DrepanidotcEnia in- 

 fundibuliformis, a tape worm 

 of the fowl. (After Stiles.) 



