102 



LECTURE VI. 



and simple in the thicker division of the body, at the posterior ex- 

 tremity of which it terminates in a contracted straight tube, whicli 

 may be called the rectum : the anus is transverse and bilabiate. 



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

 The ajsophagus {b,Jig. 44) is round, slightly bent, and suddenly 

 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 consti-iction, but it is continued of uniform 

 structure, slightly enlarging in diameter to the anus {d). The chief 

 ^g 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, Avhen 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, which probably imbibe the nutriment 

 exuded from the intestine into the general cavity of the 

 body and carry it to the four longitudinal vessels, which 

 traverse at equal distances the muscular parietes. 



The analogous processes are more highly developed in 

 the Ascaris lumbricoides, in which species I shall de- 

 scribe the digestive and nutritive apparatus more in detail. 

 The mouth {Jig. 46, 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 boumlaries 

 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 

 '^tTHcoides'" ^'^ produce the divarication of the tubercles and the open- 

 Haif nat. size. j,^g ^f ^|^g moutli : the tubcrclcs are approximated by the 

 action of a sphincter muscle. 



The oesophagus {fig. 46, b) is muscular, and four or five lines in 

 length, narrow, slightly dilated posteriorly, and attached to the mus- 

 cular parietes by radiated filaments. Its cavity is occupied by three 

 longitudinal ridges, which meet in the centre of the canal. It is 

 separated by a well-marked constriction from the second part of the 

 alimentary tube {c, c), which extends to the terminal outlet (r/) with- 



