ENTOZOA. 607 



obvious anus, and the intestines usually appear as caeca aris- 

 ing from one orifice. This tribe has been subdivided into 

 the four following groups. 



A. Head furnished with a produced snout, armed with 

 reflected bristles. This includes the following genera, 

 (forming the Acanthocephala of Rudolphi,) Echinorhyn- 

 chus, and Haeruca. 



B. Head furnished with two or four pores or processes. 

 a. Tail simple. Tenia, Scolex, Tricuspidaria, Bothryoce- 

 phalus, Horiceps, and Tetrarynchus. I- Tail vesicular. 

 Cysticercus and Caenurus. 



C. Body with one or more suckers for adhesion. Mo- 

 nostorna, Amphistoma, Caryophyllseus, Distoma, Poiysto- 

 nia, and Tristoma. 



]). No external organs. Ligula. 



In the investigation of this singular group of animals, 

 considerable assistance, in ascertaining the species, is derived 

 from a knowledge of the particular animals in which they 

 reside. Several lists of animals, with their intestinal in- 

 mates, have been published, as the one by RUDOLPHI, vol. ii. 

 part ii. p. 295 ; and a still more extensive one, as an Index 

 to the collection of ENTOZOA, at Vienna. 



II. 



R ADI AT A. 



Nervous system disseminated through the body, and not 

 appearing in the form of a collar round the gullet, nor a 

 longitudinal cord. 



The animals of this extensive division of the Invertebrata 

 invariably reside in the water. In form, they are in gene- 

 ral more or less stellular ; neither organs of hearing nor 

 sight have been detected. In the following brief view of 

 the different tribes, we shall consider them under the four 

 established classes, Echinodermatn, Aealepha, Zoophyta, 

 and Infusoria. 



