112 THE IIELMINTIIES. ^ 107. 



The food enters the cavity of the body of Echinorhyncus probably in the 

 same manner, for their skin has great power of absorption.'-^ 



The Acanthocephali have this peculiarity, that between the skin and the 

 muscular walls of the cavity of the body there is a thin layer of finely- 

 granulated parenchyma, often of an orange or yellow color, which|is traversed 

 by longitudinal and transverse canals. 



These canals, having no proper walls, form a continued vascular system, 

 and contain a liquid -filled with granules and vesicles. As this system is 

 completely closed, and cannot therefore receive nutritive substances from 

 without, it must be regarded as nutritive or circulatory, and not digestive, 

 as it has been by many naturalists. 



§ 107. 



In the other groups of the Helminthes the digestive organs are pretty 

 gerierally well developed. 



The Trematodes have a mouth situated usually upon the border of the 

 cephalic extremity, and where there is a sucker occupying its bottom. From 

 this there passes along the middle line of the neck a thin-walled oesophagus, 

 which is often of an S-like form. Directly behind the mouth or oral sucker, 

 but sometimes a short distance removed from it, the oesophagus is surrounded 

 by a round or oval muscular pharynx. '^^ From the extremity of this pass 

 off, usually, two blind intestinal tubes, which, passing along both sides of 

 the body, extend generally to its posterior extremity.*-' The other forms 

 of the digestive canal are as follows : in Monoslomum mxitabile,^'^'^ and fla- 

 vum, the two intestinal tubes, instead of ending coecally, form the arc of a 

 circle ; '■*' in Aspidogaster, a simple and uniform intestine succeeds upon the 

 pharynx, and ends in a coeeum at the posterior extremity of the body ;'^^ 

 in Gasterostomum fimbriahim, this canal is very short, and terminates in 

 the same way, but there is a mouth in the middle of the ventral surface ; 

 in Bucephalus polymorphus ,^'^'' the structure is similar; and in Pentastomum, 



similar error in regarding these organs as mouths, mum, Distomum, and Polystomum., the intestinal 



not only in Taenia and Cysticercus, but also in bifurcation extends to the posterior extremity of 



Bothriocephalus. I have been unable to find a the body. With Distomum chilostomtim, and 



mouth upon the cephalic extremity of the Cestodes, many other species of this genus living in the Neu- 



as has Mehlis (Tsis, 1831, p. 1.31), or upon that of roptera, the whole intestine is reduced to two short 



Taenia solium, as has Owen (Lcct. on the Comp. right and left coeca, which are given off from the 



Anat. &o. p. 48, fig. 21, a.). The fossa sometimes end of the oesophagus. 



found upon this last, is due to the retraction of the 3 Creplin, Nov.Observ. de Eatozois, fig. 10, 11. 



circle of hooks, or of the proboscis, withm the 4 This arrangement has been also, but errone- 



sheath. ' ously, assigned to Distnmum tereticolle ; see 



2 Most Helminthologists admit that Echinorhi/n- fVa^ner, Lehrljuch der vergleichenden Anat. 1834, 



chus receives its food through a small orifice at p. 75, and Creplin, in Ersch and Gruher^s Ency- 



the extremity of the proboscis, the sheath of the clop. XXIX. 1837, p. 314. 



last aiding in suction and deglutition. I have been This error is probably due to the inaccurate copy- 

 unable to convince myself of the existence of this ing of figures ; see Ann. d. Sc. Nat. II. 1824, p. 

 orifice, and never have found food in the cavity of 493, PI. XXIII. fig. 4, 5 ; and Schmalz, Tabulae 

 the sheath. On the other hand, I have often, like Anat. Entozoorum, Tab. VIII. fig. 2, 3. By refer- 

 Creplin and Melilis, seen Echinorhynchus re- ring to the original figure in the Memoir of Jurine 

 ceive and rejcat liquids tlirough the skin. (M6m. de la Soc. de Phys. et d'Hist. Nat. de 



1 With Distomum g-lohiporuyn, the pharynx is Geneve, II. pt. 1, 1823, p. 149, tig. 4, .5), from which 

 somewhat removed from the oral sucker ; see Bur- these have been copied, there is found no trace of 

 meister, in fViecrmann's Arch. 1835, II. fig. Taf. a closed, arcuate intestinal canal behind. More- 

 1, 3. In Distomum echinatum, militare and over, Jurine expressly says that he has seen the 

 allied species, the oesophagus is usually very intestiwdl Mies of Distomum terrcticolle,a,scoeca. 

 long, hnt in Distomiimoxi/cephalum, it is very 5 Baer, in Nov. Act. Acad. &c. XIII. pt. 1, p. 

 short ; and in DistomuTn appendiculatum, it is 536, Taf. XXVIII. ; also Diesins, 3Ied. Jahrbuch. 

 entirely wanting, and consequently the intestinal d. k. k. iisterreichischen SLaates.XVI. 1834, p. 423, 

 bifui-cation is directly behind the pharynx. fig. 8-11. 



2 In Monostomum, Amphistomu7n, Holosto- G Bucephalus polymorphus is prohahly a. larvnl 



