CESTODA OR TAPEWORMS. 67 



seem to be known in the Fowl ; their identity, how- 

 ever, is a matter of great difficulty, and much con- 

 fusion regarding the species has consequently arisen. 

 Of these twelve only two, and some doubt exists 

 here, are cysts ; all the remainder are sexual tape- 

 worms, which produce in their numbers the disease 

 known as ' Tamiosis.' 



Various Species infesting the Fowl. 



Regarding the best-known Cestodes in Fowls, we 

 will take for description three whose life-histories 

 are known : — 



(1) Davainea proglottina, Blanchard. — This worm 

 is sometimes very abundant in the Fowl's intestines, 

 generally in the duodenum. About 8 mm. long. It 

 never consists of more than four segments. The 

 scolex or head is only *10 mm. long. The segments 

 break off and live a free life in the intestine for 

 some time, growing to about 1*8 mm. long. They 

 can expand and contract, and are very lively. The 

 ova are large compared to most i tapeworms.' 



The life-history of proglottina has been traced out 

 by Grassi and Rovelli. It seems the ova are taken 

 up by various species of Slugs (Limax), and there in 

 the different organs they become transformed into 

 cysts of the Cysticercus type (fig. 21). 



The slugs are, as we know, eaten by fowls with 

 avidity. The cysts are thus released, and develop 

 into D. proglottina, with its four segments, in about 

 eight days. 



f2 



