304 



Nematoidea.- 



-ENTOZOA. Trematoda. 



«a3E®irj- 



arrangement upon that of Zeder. In the following 

 pages we shall adopt a somewhat similar method, and 

 divide them also into five orders : — 



I. Nematoid, Round Worms — those which have 

 a slender, elongated, cylindrical hody, more or less 

 filiform, and rigid or elastic. The individuals have a 

 true iii-testinal canal, and are of both sexes. 



II. AcANTHOTHECA, Sheathed - hooked Worms — 

 those which have a more or less club-shaped form, 

 with a large head and the mouth in a depression of it, 

 and surrounded with four strong, brown, simple hooks. 

 The sexes are separate. 



III. Trematopa, Suctorial or Flulce Worms — those, 

 the species of which have the body generally flat, soft, and 

 furnished with suctorial discs. They have no intestinal 

 canal, and the sexes coexist in the same individual. 



IV. AcANTHOCEPHALA, Hooked 

 Worms — those in wliich the body 

 is slender, round, subelastic, and 

 provided at the anterior extremity 

 or head with a retractile proboscis. 

 They have no intestinal canal, 

 but distinct genital organs, and 

 distinct sexes. 



V. Cestoidea, Ribband or 

 Band Worms — including the 

 Cystic Worms or Hydatids 

 [Cystica of Rudolphi) ; those 

 that have an elongated, flattened, 

 soft, continuous or jointed body, 

 and a head either round and 

 provided with a crown of small hooks, or flattened and 

 furnished with two or four suctorial pits, called hothria. 

 In these the two sexes are imited in the same indi- 

 vidual, and no trace of intestinal canal is to be seen. 

 They multiply also by fissuration. 



Order I.— NEMATOIDEA [The Round Worms). 



This is the most highly organized order of all the 

 Eutozoa, and contains a great many species. It com- 

 prises also more species found inhabiting man, than any 

 cf ths other orders. They may be defined as worms 

 with a filiform, or very long cylindrical or fusiform body, 

 covered with a resisting integument. The mouth is 

 terminal or nearly so, and the vent is nearly terminal or 

 preceding by a short distance a very slender tail. The 

 intestine is straight. The sexes are separate. In size 

 they vary much, some being scarcely a line long, others 

 measuring an inch, and .others again reaching the length 

 of a foot. The greater proportion of them are found 

 in the interior of the body of other animals, but a few 

 are detected in the muscular system. 



The most typical genus of Nematoid or Roundworms 

 is the genus Ascaris. The Ascarides are almost always 

 found in the intestines of vertebrated animals ; and one 

 species infests the alimentary canal of man. 



Order II.— ACANTHOTHECA. 



This order has been constituted to receive a few worms 

 which Cuvier arranged amongst the Nematoidea, and 



Rudolphi amongst the Trematoda, but which differ from 

 both these orders in several respects. The order may 

 be defined as composed of worms having a straight 

 intestine, with the mouth subterminal, and the vent 

 terminal. The mouth is situated on the infeiior sur- 

 face, and is armed with two pairs of hooks, which are 

 retractile into sheaths. They have a distinct nervous 

 system, and the sexes appear to be separate. 



Genus Pentastoma. — This genus is almost the 

 only one belonging to it. The species are never 

 found in the intestines; they are only to be found in 

 the frontal sinuses, in the larynx or the lungs of Mam- 

 malia and Reptiles, or in cysts or serous cavities. They 

 are worms of an oblong or cylindrical shape, pleated 

 transversely, or nearly ringed. The head is generally 

 large, and the mouth is situated on the under surface. 



Fig. 207. 



Pentastoma tfpnioidea. 



with a longitudinal slit on each side, from which issue 

 two pairs of simple or double hooks, retractile into as 

 many distinct cavities. The genus is represented by 

 a figure of Pentastoma tcenioides. — See fig. 207. 



Ordek III.— TREMATODA. 



This is a very natural order of intestinal worms. They 

 are more or less elongated, and of a depressed form, 

 and provided with one or more organs of adhesion or 

 suckers, by means of which they attach themselves to 

 the various animals upon which they live as parasites. 

 They are provided with a mouth and an intestine, but 

 have no vent. The two sexes are united in the same 

 individual. In those species which have been particu- 

 larly watched the ova are elliptical, and the embryos 

 when first hatched are generally covered with vibratile 

 cilia, and undergo distinct metamorphoses in their pro- 

 gress to maturity. The Trematodes are found in the 

 various cavities of the body, in the tissue of certain 

 organs, or even on the surface of the body ; and exist 

 in both vertebrate and invertebrate animals. 



The various species which are found adhering to the 

 external surface of the animals upon which they live, 

 forming the families Onchobothriidce and Capsalidcv, 

 have, in consequence of their being outside parasites, 

 been placed by several naturalists in the class Annelida. 



Genus Distoma or Flul-e-wnrms, the species of 

 which are all found internally, may be taken as the 

 type of the family. The body of these worms is gene- 

 rally depressed, sometimes of a cylindrical form, and is 

 provided with two distinct and isolated suckers, one 



