ANATOMY OF THE NEMATODES 



265 



the mid-gut, which is likewise cellular. The so-called mid-gut is 

 a tube lined by flat, cubical, or cylindrical cells (fig. 182), which 

 has no outer mesodermal layer (connective tissue, muscles) ; its 

 transverse section is circular or flattened dorso-ventrally ; the 

 lumen may run in a straight line, or it may form sinuosities 

 amongst the alternating prominences of the then flat epithelial 

 cells. 



The ectodermal hind-gut is, as a rule, very short ; very fre- 

 quently there is no cellular lining, so that it consists only of a 

 cuticular tube, which in large species is surrounded by circular 

 muscles. In some species there are special bundles of cutaneous 

 muscles along the entire gut, or at least on the terminal gut. 

 There is sometimes a retrogression of 

 the alimentary tube in the adult stage 

 of a few parasitical species. 



Intestinal caeca and cesophageal glands 

 sometimes appear as intestinal append- 

 ages ; the former are cylindrical orgaAs 

 of various size, running backwards or 

 forwards, and arising from the posterior 

 extremity of the oesophagus. They are 

 lacking in many species. The ceso- 

 phageal glands are unicellular ; a dorsal 

 and two subventral glands may be dis- 

 tinguished according to their position ; 

 as a rule they open into the oesophagus 

 at a distance from one another. The 



glandular body lies in the bulb of the oesophagus, the dorsal ones 

 in the cul-de-sac arising from it. 1 



THE NERVOUS SYSTEM of the larger species of Ascaris is the only 

 one sufficiently known ; '' it consists of a pharyngeal ring con- 

 taining 50 60 fibres closely surrounding the oesophagus (fig. 184), 

 various groups of ganglion cells, and a certain number of nerves 



FIG. 184. Transverse sec- 

 tion of anterior end of the 

 body of Ascaris lumbricoides 

 with the nerve ring surround- 

 ing the oesophagus. (Enlarged.) 



1 Jagerskiold, L. A., " Beitr. z. Kenntn. d. Nemat." (Zool. Jahrb. Anat., 1894, Part 

 vii., p. 449). " Ueb. d. (Esophagus d. Nemat." (Bih. K. Svensk. Vet.-Akad. HandL, 

 1897, xxiii.-iv., No. 5). Looss, A., " Ueb. d. Ban d. (Esoph. bei einig. Ascar." (C. /. 

 B., P. u. I., 1896 [i], xix., p. 5). 



2 Biitschli, O., "Beitr. z. Kenntn. d. Nervens. d. Nemat." (Arch. /. mikr. An., 1874, 

 x., p. 74). " Zur Herleitg. d. Nervens. d. Nemat." (Morph. Jahrb., 1885, x., p. 486). 

 Rohde, E., "Beitr. z. Kenntn. d. Nemat." (Zool. Beitr. [A. Schneider], 1885, i., p. n). 

 Hesse, R., " Ueb. d. Nervens. v. Asc. megaloceph." (Z. f. w. Z., 1892, liv., p. 548). 

 Apathy, St., "Das leit. Elem. in d. Muskelf. v. Ascaris" (Arch. f. mikr. An., 1894, 

 xliii., p. 886). Brandes, G., " Das Nervens. d. als Nemathelm. zusammengef. Wurm- 

 tyf>." (Abh. d. naturf. Ges. Halle., 1899, xxi., p. 273). 



