676 DR. H. CHARLTON BASTIAN ON TILE ANATOMY AND PHYSIOLOGY 



exists, is terminal, though in some species another may be present near the middle of the 

 a^sophagus, or one in this situation may be the only swelling met with. These enlarge- 

 ments, again, may be either simple developments of the muscular walls, or in addition 

 they may contain in their interior a more or less complex apparatus of homy chitinou.s 

 plates. The simple terminal swelling may be seen amongst the free Nematoids in the 

 genus Spira, whilst homy plates of gradually increasing complexity are seen in the genera 

 Aphelenchus, Cephalohus, Anguillula, Rhahditis, and Flectus, and to continue the series 

 amongst the parasitic species, in Ileterakis, Oxyuris, and many others. In Bhabditvi 

 there is in addition a simple, central, elongated swelling, whilst a somewhat globular 

 enlargement exists in this region only in the genera Tylenclms and Diplogaster* . 



The terminal developments have generally been named and described as stomachs, the 

 internal homy plates being looked upon as a kind of teeth, but, as I have on a former 

 occasion pointed out, there seems little warrant for this belief. No dilatations of the 

 central cavity of the organ are met with in these situations, merely an hypertrophied 

 condition of the muscular walls, and the homy plates, instead of being called " tooth-like, 

 crushing organs "t, should, I think, be considered as rather valvular in their nature ; the 

 whole apparatus being principally destined to facilitate the taking of food, though partly, 

 perhaps, also more effectually to prevent the regurgitation of the intestinal contents 

 during the movements of the animal. The Xematoids have no prehensile organs of any 

 kind, and their food is, I believe, principally taken by a process of suction. The simul- 

 taneous or successive contraction of the transverse radiating fibres, throughout the length 

 of the oesophagus, producing a dilatation of its central canal would cause an inrush of 

 any food or fluid matter to which the mouth might be applied. I have often seen the 

 passage of fluid along the oesophagus of the free Nematoids in this way ; the muscles 

 contract with the greatest rapidity, and in Bhahditis marina I have seen the valvular 

 plates open and shut just as quickly to give passage to the fluid. Whether the tooth- 

 like projections from the pharyngeal cavity in the Oncholaimi are capable of movement 

 I cannot say ; I, at least, have never seen them move, and they appear closely adherent 

 to the walls of their enclosing cavity. In Tylenchus and Aphelenchus the lumen of the 

 oesophagus is very narrow, and apparently stiff" and cord-like in external appearance. 

 This misled Davaine, so that he did not recognize its real nature in Tylenchus tritici, 

 but spoke of it as " un filament simple, tres distinct, semblable a une fibre de tissu 

 elastique" proceeding from the stylet, and whose object he thought was "de doimer de 

 la force et de la resistance a I'extremite anterieure de I'animal":};. 



The best examples of the cellular or glandular structure of the oesophagus are met 

 with in the genera Trichosoma and Trichocephalvs, and in Trichina spiralis, though I am 

 unable to agree with Ebebth with regard to some of the details of their anatomy. 

 The first portion of ihe oesophagus behind the mouth, in these animals, is different from 

 the remainder, it is narrow, and seems to have granular rather than ceUular contents. 



* See " Monograph on the AnguillulidsB " for figures. t Cobbold, Entozoa, p. 367. 



4: Keeherches sur rAnguillule du ble nielle, 1857, p. 24. 



