BOOK FIFTH. 
HELMINTHES. 
CLASSIFICATION. 
§ 99. 
Ir is very difficult to characterize the class Helminthes, 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, Anthocephalus. 
ORDER II. CESTODES. 
The parenchymatous body 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: Gymnorhynchus, Tetrarhynchus, Bothriocephalus, Taenia, Tri- 
aenophorus, Ligula, Caryophyllaeus. 
1 Anguilluia 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 forma of these last. 
3ts hook and suckers, strikingly resembles that of 
