208 ON AUSTRALIAN ENTOZOA, 



Class. HELMINTHES. 



It is very difficult to characterize the class Helminthes, for 

 it contains 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 form of a bladder, and filled with a 

 serous liquid. Digestive and genital organs are wanting. 



Genera : EcMnococciis, Coeiiurus, Gysticercus, A'lithroceplialus. 



Order II. Cestodes. 



The parenchymatous body is riband like, having often incom- 

 plete transverse fissurations ; often it is wholly divided trans- 

 versely into rings. Digestive organs are wanting. The genital 

 organs of both sexes are combined in the same individual, and 

 generally are often repeated. Copulatory organs are present. t 



Genera : Gymnorhynchus, Tetrarlynclms Bothriocephalus, 

 Tcenia, TricBnoiolwrus, Ligula, Garyophyllmos. 



* Nearly all the genera of their order are considered to be young 

 tape-worms. — G.K. 



t Von Siebold has changed his opinion, and states some years later 

 " On the Tape and Cystic worms." (translated by Professor Huxley, London, 

 1857, page 40)." The sexually matured individuals of the Cestoidea are no 

 other than their full grown joints in which are developed the male and 

 female genitalia, by whose co-operation eggs capable of reproduction are 

 generated, and the continuation of the species is secured. Such a sexually- 

 mature hermaphrodite joint of a cestoid worm which separates from the body 

 of the scolex with great readiness, is denominated a Proglottis. The formation 



