104 ENTOZOA. 



CHAPTER VIII. 



OBSTODA. 



Cestoda or TapeAvorms — General characters and habits — Distribution in mammals, birds, 

 reptiles, and fishes — Estimated number of species — Tseniadte— Particular account of 

 the development of Cysticercm pmformis from the eggs of Tcenia sei-rata, and also 

 of the adult tapeworm from the Cysticercus — Constitution of the " zoological indi- 

 vidual" — Genera. 



The fifth order of Helminths comprises aU those familiar forms of 

 anenterate parasites commonly called tapeworms ; and I may 

 remark, in passing, that it was Rudolphi who first designated this 

 group Cestoidea (A;eo-T09, a girdle ; etSo?, form), fi:'om the charac- 

 teristic shape displayed by the several species. These animals, 

 therefore, are readily distinguishable by their soft, flat, elongated, 

 semitransparent bodies, which are usually segmented or divided 

 by transverse lines into a number of joints. The anterior or 

 first joint, properly speaking, forms the so-called head. This head 

 is furnished with suckers for the purpose of fixing the parasite to 

 the walls of the intestine of the animal in which it is lodged ; the 

 anchorage being often rendered more secure by the development of 

 a special hook-apparatus. 



The tapeworm may be looked upon as a creature compounded of 

 a series of partly dissimilar animal forms closely linked in single file ; 

 and the welfare of this peculiarly associated colony is, in a great 

 measure, dependent on its connection with the so-called head. On 

 the other hand, viewing the subject philosophically— with due regard 

 to the excellent rule which makes the " zoological individual " to 

 consist of the total products of a single ovum — the entire tapeworm 



