25 



skin is seen in the form of lateral serrations. But these trans- 

 verse markings must not be confounded with true segments, 

 being merely due to folding of the loose and inelastic epidermis. 



Alimentary System. 



The mouth 1 opens into a strong, muscular pharynx, which 

 is thicker posteriorly. At the hinder end, this is separated 

 by a constriction from the oesophagus 2 . Internally, at this 

 spot, there is a chitinous lamella, or diaphram. 



The oesophagus is cylindrical, but its cavity is triangular, 

 with strong cartilaginous seams at the angles. Three power- 

 ful, external muscles maintain its triangular form. It is 

 divided by another constriction from the stomach. 



The stomach is a very muscular organ. Its cavity is also 

 prismatic, but dilates posteriorly. It is furnished with three 

 strong, pointed, chitinous cones, or teeth. These are em- 

 bedded in the muscular walls, and their points project into the 

 cavity of the organ. 



The intestine is marked off from the stomach by another 

 constriction. It first turns forward ; and then runs almost 

 straight to the anus, and nearly in the middle line of the worm. 

 It is but slightly convoluted. 



Throughout its length, the alimentary tract consists of 

 three chief layers. These are : inner and outer (peritoneum) 

 epithetial layers, and a middle muscular layer. An inter- 

 mediate layei of cells in the intestine have had a hepatic 

 function ascribed to them. 



The rectum does not show these three layers, but has 

 muscles which open and close the anus. 



Nervous System. 



The nervous system is divided into central and peripheral 

 portions, the former including the encephalon, the oesophageal 



1 Various theories have been 2 Several observers have at- 



advanced as to the threadworm's tempted to trace breathing-appara- 



mode of obtaining nourishment tus, but without success : " Jusqu' 



" M. Marc hand arrive a ce resultat ici il a ete impossible de determiner 



singulier : que la nutrition s'opere des organes pour la respiration." 



chez les oxyures par la surface (PASQUIOU, F. M., Des helminthes 



externe de la peau, comme celle vivant dans le tube digestif, Paris, 



des Acephalo-cystes." (GERVAisand 1805, p. 5.) 

 VAN BENEDEX, Zooloyie Medicate, 

 vol. ii., p. 128.) 



O. V. r 



