868 ACALEPHA. 
of the animals which they inhabit. No trace of circulating vessels has been 
detected ; and the vestiges of nerves are so obscure, that many naturalists 
have doubted their existence. When these characters are found in an ani- 
mal similar in form to those of this class, it is arranged along with this 
division, though it does not inhabit the interior of another species. 
Linneus arranged this group of animals ina division of his great class 
Vermes, including the genera Lwmbricus, Sipunculus, Fasciola, Gordwus, 
Ascaris, Hirudo, and Myzine. Subsequent writers, such as Pallas, Muller, 
Blumenbach, Bloch, and Gaze, established new genera, or added new spe- 
cies; and more lately, Cuvier, Lamarck, Rudolphi, and Bremser, from more 
detailed examination of the animals, and a more intimate knowledge of their 
structure, have proposed arrangements better suited to the present state of 
the science. 
M. Lamarck divides the class into three orders, viz. Hispide, Rigidule, 
and Mollasse, the last of which is subdivided into three sections. In the. 
method of Cuvier, the class forms two orders, Les Cavitaires, and Les Paren- 
chymateaux, according to the structure of their body. And Rudolphi, in 
his work, entitled Entozorum, sive Vermium Intestinorum Mstoria Naturalis, 
arranges them into five orders, viz. 1. Nematoides; body elongated, cylin- 
drical, elastic. 2. Acanthocephalus ; body cylindrical, slightly elastic, with 
anterior simple or compound, prolongation covered with a series of bentand 
retractile spines. 3. Trematodes; body flattened, or slightly cylindrical, 
soft, and provided with pores for suction. 4. Cestoidea; body elongated, 
flattened, soft, of one or many pieces. 5. Cisticorus; body terminated by 
or adhering toa vesicle. This arrangement includes besides, three isolated 
genera, which would not admit of being placed under the previous heads. 
Latreille, in his Familles du Régne Animal, disposes the intestinal worms 
chiefly after the methods of Rudolphi and Cuvier ; combining in his sketch of 
the class, the general views of these excellent naturalists. As the method 
of Latreille is here followed with one exception, it is not necessary to repeat 
the characters of the subdivisions. That branch of natural science which 
treats of intestinal worms, is generally termed Helminthology. 
CLASS XII.—ACALEPHA. 
Body gelatinous, circular, and radiated, with the skin soft and transparent, 
susceptible of contraction and dilatation. 
Tue class Acalepha of Cuvier embraces the Radiaires, Medusaires and Ano- 
males of Lamarck, and besides includes the genus Actinia, which the latter 
