574 DE. H. CHAELTON BA8TIAN ON THE ANATOMY AND PHYSIOLOGY 



Angiostoma, Syngamus, and Anchijlostoma, whilst it is long and cylindrical in iMspharagus, 

 and rudimentary in the genera Ileterakis, Stenodes, Stenurus, Spiroptera, and Strongylu^. 

 In all, this cavity is lined with more or less strong chitinous walls, more developed in 

 some situations than in others, so as to form horny plates or even tooth-like projections. 

 The homy plates may be well seen in the members of the genus Cucullamis. In Anchy' 

 lostoma duodenale, according to Kuchenmeisteb, there are four strong teeth projecting 

 from the upper wall of the pharynx, whilst Siebold describes the entrance to the pha- 

 ryngeal cavity in Strongylua armatus, S. hypostomiis, S. dentatus, and 6'. tetracanthm as 

 "garnie d'un cercle de dents comees," and adds, "il existe des muscles speciaux pour 

 les mettre en mouvement." Amongst the free Nematoids*, the most distinct pharyngeal 

 cavities with horny capsules exist in the genera Mononchus and Oncholaimus, the former 

 having one tooth-like projection and the latter three ; it is rather long and cylindrical in 

 Bhabditis, somewhat pear-shaped in Sphoerolaimus, cup-shaped with horny projections 

 from its base in IHplogaster, and exists with more flexuous walls in the genera Idnhomoem, 

 CyatJwlaimus, Spilophora, and Ckromadora. In the last two genera three homy apo- 

 physes extend backwards from the pharyngeal cavity, which are extremely well deve- 

 loped in Spilophora robusta. In the genus Enoplus three well-marked and separate teeth 

 exist in the pharyngeal region, though I have never been able to make out their exact 

 relationship to the commencement of the alimentary canal. In the genus Dorylaimus 

 the pharynx is modified into a strong hollow spear-like body, and can be protruded for 

 some distance from the mouth by means of special muscles (Plate XXVIII. fig. 3) which 

 move it in common with the anterior part of the oesophagus. In all immature species 

 of this genus, a reserve spear exists in the substance of the oesophagus a short distance 

 behind, and of a slightly larger size than the one in situ, whose place it subsequently 

 takes. I shall refer to this subject again in the section on development. In the genera 

 Aphelenchus and Tylenchus a spear-shaped homy phaiynx also exists, simple in the 

 former, but having a trilobed base in the latter, though in neither of them is there 

 present the reserve spear met with in the Dorylaimi. Most likely these spears are exsertile 

 also, though I cannot speak from actual observation ; they suggest a resemblance to the 

 " sharply-pointed dentule "f, capable of being exserted from the mouth in some species 

 of the genus Mermis, whilst what is met with in the Dorylaimi recalls the principal and 

 reserve proboscideal spines in the members of the genus Tetrastemma^ and other of the 

 Nemertid(B. 



In those species in which no pharyngeal cavity exists, the mouth communicates at once 

 with the oesophagus. Besides innumerable variations in detail, two principal modifica- 

 tions in the nature of this portion of the alimentary canal are met with in the Nema- 

 toids, inasmuch as in nearly all the parasitic forms, and in about one-half of the free 

 species, it has a well-developed muscular structure, whilst in the genera Trichinu, Tri- 



* The different modifications now to be mentioned are figured, and described more fully in the " Monograph 

 on the AnguiUulidce" Trans, of Linn. Soc. vol. xxt. 



t CoBBOLD, Entozoa, 1864, p. 61. :t Cabus, Icon. Zootom. tab. viii. 10. 



