NEMATODA DIGESTIVE SYSTEM I 3 I 



lips are well provided with sense papillae. The mouth leads into 

 an alimentary canal, which with hardly an exception runs straight 

 through the body to the anus without twists or loops. The anus 

 is usually placed ventrally and is not terminal, but in Trichina 

 and Trichocephalus it is at the end of the body, and in Mermis, 

 where the several parts of the alimentary canal are said not to 

 communicate, it is absent altogether. Ichtltyonema, Dr avunculus, 

 Allantonema, Atractonema, and other Filariae are also aproctous. 



The alimentary canal is divisible into three parts (i.) the 

 oesophagus, (ii.) the intestine, and (iii.) the rectum. The suctorial 

 oesophagus is a very muscular, thick - walled tube, lined with 

 cuticle continuous with that which covers the body, and like it 

 cast from time to time. Its lumen is usually much reduced, and 

 is almost invariably triangular or triradiate in section (Fig. 62). 

 In many genera the hinder end of the oesophagus is swollen into 

 a muscular bulb, which is armed with teeth in Heterakis, Oxyuris, 

 Pelodera, Leptodera, etc. Other species, such as Tylenchus, Aphel- 

 enchus, Dorylaimus, are armed with a spear, which in Onyx} 

 a genus recently described and allied to the last named, is borne 

 on a special bulb. The use of the spear is to pierce the tissue 

 upon the juices of which the animal lives. A gland lies embedded 

 in the thick walls of the oesophagus, and opens into its lumen 

 by a fine tube. This was first described by Schneider 2 in A. 

 megalocephala, and more recently it has been found by Hamann 3 

 in a number of Ascaridae and Strongylidae from the Adriatic, and 

 also in Lecanocephalus. 



With a few exceptions, such as Mermis, where it is blind, the 

 oesophagus opens posteriorly into the intestine. This is a some- 

 what flattened tube, whose shape and position are often altered 

 by the development of the generative organs. Its wall consists of 

 a single layer of columnar cells, with large nuclei coated internally 

 and externally by a layer of cuticle. The inner layer of cuticle 

 is usually perforated by very numerous minute pores. In some 

 species the intestine is degenerate, in Mermis it is a closed tube 

 opening neither into the oesophagus nor into the rectum ; in 

 Trichina spiralis and in the larva of Tylenchus tritici it consists 

 of a single row of cells perforated by a duct, but in the adult of 



1 N. A. Cobb, P. Linn. Soc. tf.S. Wales, 2nd ser. vol. vi. 1891, p. 143. 



2 Monographic der Ncmatodcn, Berlin, 1866, p. 192. 



3 Zool. Anz. vol. xvi. 1893, p. 432. 



