ORDER'. Entomoida, Latreille (from *promo insecta).
The animals belonging to this order were termed Epizoaria by Lamarck from the parts of the body to which they are generally found attached, and he comprehended them under the three great genera Entomoda, Lernaa, and Chondracanthus, which have since been much subdivided. The term En tomoida is applied to them by Latreille, and points out their remarkable affinities to the class of insects in the divisions of their body and in their external organs. They form a link of transition from parasitic insects which move freely to and fro on the surface of animals, to the true entozoa which remain deeply buried in the substance of their bo dies. In their articulated appendices some of the species, particularly of the Lemma, have a close resemblance to the branchiopodous crustacea. The Entomoida are found attached only to the surface, or partially buried in the superficial soft parts of aquatic animals, while the rest of their body hangs constantly exposed to the action of the external element. From this partially exposed situation they partake of a mixed life, and exhibit a combination, in the same individuals, of the forms and organs both of insects and intestinal worms. Like these worms they possess a very simple inter nal organization, a soft, elastic, naked, and feebly irritable body; they are permanently fixed to the animals on which they feed, and they live by suck ing the internal fluids. From their external situation they have not only organs for piercing and sucking the animal substance like entozoa, but also parts variously constructed for attaching themselves to the surface of the body like insects. Some possess piercing organs, placed on appen dices extending like tentacula from the head, some present at the sides of their prosbocis the rudiments of jointed antenna, and some of the species are said to have sessile eyes. They possess a tough elastic integument, distinct muscular and nervous filaments, a simple intestinal canal, with a mouth and anus distinct. The mouth is in form of a pro
boscis, and is generally provided with curved hooks, tentacula or antenna. Their two ovaria hang externally from the posterior extremity of the body, and in several of their characters the Ento moida are allied to the parasitic branchiopodous crustacea, but they present no appearance of bran cilia or other organs of respiration, and they do not appear to change their external covering like crustacea. The structure of these singular parasitic animals is still very imperfectly known. M. Blain ville has published an interesting memoir on the structure and classification of these animals in the Journal de Physique for 1822, and Professor Grant has described the anatomy of a remarkable species from the Arctic seas, in the Edinburgh Journal of Science, Vol. VII. The following genera of this order have been chiefly formed by AI. Blainville from the subdivision of the three great genera already mentioned, and they have been recently adopted by Latreille, viz.
The worms belonging to this extensive order, are chiefly characterised by the lengthened, slender, and cylindrical form of their body, and by their total want of sharp recurved spines around the mouth. From their want of spines or teeth, they are termed by Latreille Anodonta. They have a simpler form and internal structure than the pre ceding order, their mouth presenting no rudi mentary antenna or other appendices, and al though the nervous system in some of the species is allied to that of the annelides, they do not pos sess seta or other organs of motion extending from the sides of the body. The body is covered with a smooth elastic integument, within which are a transverse and a longitudinal layer of mus cular fibres. The intestinal canal has a mouth and arms placed at its opposite extremities, and the sexes are on separate individuals. The Guinea worm (Filaria Medinensis) is the type of this or der, and it comprehends according to Rudolphi the following genera.