ENTOZOA. 103 



out presenting any natural division into stomach and intestine. The 

 lower third of the tube is the widest. Numerous long pyriform villi 

 project from the mucous lining of the alimentary canal. Many 

 minute filaments pass from the intestine to the soft obtuse papillae 

 which project from the walls of the abdomen into that cavity, and 

 which are called "the nutritious appendages" by Cloquet.* The 

 nutriment which these processes or appendages are presumed to 

 imbibe, is collected, according to the same author, into two canals, 

 situated each in a narrow tract of opaque substance, which extends 

 along the sides of the body, and has sometimes been mistaken for a 

 nerve, and which Vallisnieri believed to be a trachea. Morren has 

 lately described and figured the nutritive appendages as hollow ve- 

 sicles : he calls them " Vesicules aeriejines" because, he says, " they 

 evidently subserve respiration by furnishing air to the blood." Few 

 physiologists are likely to acquiesce in this view, which makes the 

 respiratory apparatus of an animal having no other atmosphere than 

 the mephitic gases of the intestinal tube, the largest and most ex- 

 tensively developed organ in the whole body. 



With reference to the organisation of the nematoid Entozoa, not 

 parasites of the human subject, I shall limit my remarks to those 

 structures which offer interesting approximations and analogies to 

 the organisation of higher vermiform animals, and of the existence of 

 which we must have remained ignorant if our attention had been 

 wholly confined to the human Entozoa. 



The entry to the mouth is beset by a circle of horny teeth in the 

 Strongylus armatus,- Sir. dentatus, and Str. tetracanthus, for the 

 movements of which special muscles are provided. In Spiroptera 

 strorigyhna the whole inner surface of the elongated mouth is pro- 

 vided with a spirally disposed horny ridge. The horny apparatus by 

 which the mouth in CiiciiUanus is opened and closed is very com- 

 plex.f The pharynx is unusually long in some nematoids, e. g. the 

 Trichocephali : and in Trichosoma Falconum it is divided into many 

 successive segments : it has sometimes a horny scabrous lining. 



I may next refer to a secreting apparatus, consisting of four slender 

 blind tubes, each about two lines in length, which are placed at equal 

 distances around the commencement of the alimentary canal in the 

 Gnathostoma spinigerum, a small nematoid worm closely allied to 

 Strongylus, which I discovered in the tunics of the stomach of a 

 tiger.J The mouth of this Entozoon is a vertical fissure, bounded on 

 each side by a jaw -like lip, the anterior margin of which is produced 

 in the form of three straight horny points. The secerning tubes 

 terminate at the mouth by their smaller extremities, and there pour 



* LXXVm. t XXIV. p. 131. X LXXXVIIL 



II 4 



