164 CLASS V. 



ledge it to be unnatural. RUDOLFIII, to whose investigation this 

 part of Zoology is so greatly indebted, compares tlie class of the 

 intestinal worms to a Fauna, a collection of animals that live in a 

 certain region. Their country is the living body of other animals. 

 Recent observations have, however, taught us that some species in 

 the cycle of their developments, leave their country for a time. The 

 radial type, which we observed in the former classes, particularly 

 .in the Polyps and Acalephs, is here wanting. All Entozoa approxi- 

 mate to the elongated form of the articulate worms, although in 

 some of them that form, on account of a bladder to which they are 

 affixed by their extremity, is not at first sight apparent. Special 

 respiratory organs are wanting. Some are entirely without sex, 

 and are propagated by gemmation ; others are bisexual ; in others 

 the sexes are distinct. 



We must premise something as to the division of the Entozoa. 

 KUDOLPHI adopts five principal sections, which had been already 

 distinguished by GOETZE and ZEDER before his time. The first is 

 that of Cystic worms (Cystica from KVO-TIS, a bladder). The body is 

 compressed or cylindrical, the posterior part of it passing into a 

 bladder ; sometimes many such entozoa are fixed on one bladder. 

 The head has suckers, a circlet of hooks, or four proboscides armed 

 with hooks. No genital organs have been discovered; nor any 

 intestinal canal. [These have been shewn to be imperfectly deve- 

 loped Teenies.'] The second division contains the Tape-worms 

 (Cesto'idea, from KCO-TOS, a girdle, a band, eldos, form). They have an 

 elongated, compressed or flat body that is mostly jointed. The head 

 has suckers ; all the individuals are bisexual ; an intestinal canal is 

 wanting. The third division is formed by the Suctorial Worms 

 (Trematodes, r/j^/iaroJS?/?, perforate). The body is soft, compressed 

 or roundish, and provided with one or more suctorial pores. The 

 intestinal canal has in general only one opening, and is usually 

 branched ; it lies in the tissue (parenchyma) of the body, not in a 

 free space. The genital organs of both sexes are united in the 

 same individual. The fourth division is that of the Thorn-headed 

 Worms (Acanthocephala, from a*ai/0a, a thorn, and ^$0X77, head) ; 

 they have a cylindrical, pouch-shaped body. The sexes are 

 distinct ; an intestinal canal is wanting. The fifth division includes 

 those intestinal worms which have an intestinal canal, with both 

 mouth and anus, suspended freely in the cavity of the body. The 



