ENTOZOA. 



69 



oesophagus suddenly dilates into the stomach, which is fusiform, and 

 indicates the beginning of the intestine by its posterior contraction. 



Tlie mouth of the Trichocephalus dispar is small and orbicular ; 

 the oesophagus is narrow and short ; the intestinal tube is narrow 

 and sacculated, where it occupies the filiform division of the body, 

 dilated and simple in the thicker division of the body, at the pos- 

 terior extremity of which it terminates in a contracted straight tube, 

 which may be called the rectum : the anus is transverse and bi-labiate. 

 In the Strongyhis gigas the mouth is surrounded by six papillae. 

 The oesophagus (b,Jig. 30.) is round and slightly contorted, and sud- 

 denly dilates at the distance of about an inch from the mouth into 

 the intestinal canal (c) ; there is no gastric portion marked off in 

 this canal by an inferior constriction, but it is continued of uniform 

 structure, slightly enlarging in diameter to the anus (rf). The chief 

 31 peculiarity of the intestine in this species is that it is a 



four-sided and not a cylindrical tube, and the mesenteric 

 processes pass from the four longitudinal and nearly equi- 

 distant angles of the intestine to the abdominal parietes. 

 These processes, when viewed by a high magnifying 

 power, are partly composed of fibres, and partly of strings 

 of clear globules, which appear like moniliform vessels 

 turning around the fibres. The whole inner surface of 

 the abdominal cavity is beset with soft, short, obtuse, 

 pulpy processes, Avhich probably imbibe the nutriment 

 exuded from the intestine into the general cavity of the 

 body and carry it to the four longitudinal vessels, whieli 

 traverse at equal distances the muscular parietes. The 

 analogous processes are more highly developed in the 

 Ascaris liimbricoides, in which species I shall describe the 

 digestive and nutritive apparatus more in detail. 



The mouth {Jig. 31, a) is surrounded by three tubercles, 

 of which one is superior, the others inferior ; they are 

 rounded externally, triangular within, and slightly granu- 

 lated on the opposed surfaces, which form the boundaries 

 of the oral aperture. The longitudinal muscles of the 

 body are attached to these tubercles ; the dorsal fasciculus 

 converges to a point to be inserted into the superior one ; 

 the ventral fasciculus contracts, and then divides, to be 

 inserted into the two which are situated below. By 

 means of these attachments the longitudinal muscles serve 

 to produce the divarication of the tubercles and the open- 

 ing of the mouth : the tubci'cles are approximated by the action of a 

 sphincter muscle. 



F 3 



Ascaris lumbri 



coidcs. 

 Half nat. si/.P. 



