BOOK FIFTH. 

 HELMINTHES. 



CLASSIFICATION. 



§ 99. 



It is very difficult to characterize the class Helrainthes, for it con- 

 tains animals having widely dissimilar organization. On this account, the 

 separation of its groups, and their distribution among the other classes of 

 the invertebrata, has been attempted. But such various difficulties have 

 arisen from this, that for the present, it is best that all these animals 

 should remain together. If a common character is not furnished by their 

 structure, it must be sought for in their manner of life ; for nearly all 

 are parasites, ^^' and during their whole life, or at least during some of its 

 periods, seek their abode and nourishment in or upon other living animals. 



ORDER I. CYSTICI. 



The body is swollen in the form of a bladder, and filled with a serous 

 liquid. Digestive and genital organs are wanting.^^^ 



Genera : Echinococcus, Coenurus, Cysticercus, Anthocejjhalus. 



ORDER 11. C EST ODES. 



The parenchymatous bod}^ is riband-like, having often incomplete trans- 

 verse fissurations ; often it is wholly divided transversely into rings. Di- 

 gestive organs are wanting. The genital organs of both sexes are com- 

 bined in the same individual, and generally are often repeated. Copulatory 

 organs are present. 



Genera : Gymnorkynchus, Tetrarhynchus, Bothriocephalus, Taenia, Tri- 

 aenophorus, Ligula, Caryopkyllaeus. 



1 Anguillula is the only exception to this. some Cestodes ; from which it might be inferred 



2 The head of the sexless Cystici, as to its form, that they are only the larval forms of these last, 

 its hook and suckers, strikingly resembles that of 



