580 DE. H. CHAELTON BASTIAN ON THE ANATOMY AND PHYSIOLOGY 



alterations by mutual pressure, seems generally to be the form in the free Nematoids, 

 together with the Trichocephali and their allies. In these animals the separate cells are 

 often most distinct, and with their fellows produce a well-marked tessellated appearance, 

 though in others the boundaries of the several cells cannot be recognized, and an intes- 

 tinal sheath of thickly disposed granules is all that can be detected. The separate 

 cells are very small in Enoplus JDvjardinii, and very large in Monhystera amMgua and 

 M. dis^uncta*, whilst they appeared almost absent, or at least free from granules, in Spi- 

 lophora costata, and in some specimens of Leptosomatum elongatum. In Symplocostoma 

 longicolle the arrangement of the cellular layer in old specimens is often most irregular. 



According to Ebekth a well-marked cuticle exists bounding the cells internally in 

 Sclerostomum dentatum, as well as in Strcmgylus commutatus and S. tenuis ; whilst in 

 the Trichocephali he says he has seen this, after the application of water, appear to be 

 composed of a closely-packed row of little rod-like bodies. He further says that 

 towards the end of the intestinal canal of the latter animals, he has recognized trans- 

 verse muscular fibres in the larger species. 



The terminal portion of the intestine, which some have named the rectum, loses the 

 cellular layer, contracts in calibre, and appears for some distance to be encircled exter- 

 nally by muscular fibres, which probably have a sphinteric function (Plate XXV. figs. 

 5, b), and with which, also, certain other muscular fasciculi, passing to the walls of the 

 body and having a dilating function, are connected. The structureless walls of the 

 rectum are continuous at the transverse anal cleft with the chitinous integument, so 

 that we may perhaps consider the structureless bounding membrane of the intestine 

 to be a modification of this tissue. 



Hitherto many doubts have been entertained as to whether or not an anal orifice 

 existed in the Guineaworm {I^racunculus medinensis), and in my paper on the anatomy 

 of that animal, I stated that I had traced the intestinal canal to what appeared to be its 

 termination close to the posterior extremity of the animal, in the centre of the great 

 ventral, longitudinal muscular band — corresponding pretty closely in situation to the 

 place where Rudolf Wagnek stated that he had seen an actual aperture through the 

 integument. I have lately examined other well-preserved specimens of this animal, and 

 have succeeded in detecting a minute aperture through the integument opposite the 

 position to which I again traced the termination of the intestine internally (Plate XXVII. 

 fig. 20, a). This aperture is, however, altogether abortive, and by no means proportionate 

 in size to that met with in other Nematoids. Indeed the development of the intestinal 

 canal as a whole appears by no means to have kept pace with the development of other 

 parts of the body. The termination of the alimentary canal is fixed in position by fibres 

 passing to it from the lateral intermuscular spaces of the animal. In the embryos of one 

 of these other specimens of Dracunculus that I have lately examined, which seemed to 

 be in a more developed condition than any I had before met \nih, I distinctly found 

 the intestine provided with an anal aperture slightly anterior to the level of the lateral 



* Trans, of liim, Soc. vol. xxv. pis. ix. & xii. 



