564 DE. H. CHARLTON BASTIAN ON THE ANATOMY AND PHYSIOLOGY 



the transverse processes are by no means necessarily absent in these same animals, as T 

 have well seen in A. osculata. In this species there is a distinct slightly sinuous inter- 

 space between the two great longitudinal muscles in the mid dorsal and ventral regions 

 in the usual situation of the longitudinal lines, and the transverse muscular prolonga- 

 tions are seen tending towards it, over which some of those from opposite sides unite 

 with one another instead of having a common attachment to the ordinary longitudinal 

 projections of the skin in this situation, whilst others seem to bend down to attach 

 themselves to the skin exposed in this muscular interspace. 



In Prosthecosacter injlexus the muscle-cells, when seen in transverse section, are found 

 to be extremely narrow as compared with their depth, and present the appearance of 

 closely packed bundles with the usual transverse markings (Plate XXVII. fig. 5). But 

 whether these animals are to be looked upon as Platymyarice or Colomyarice seems alto- 

 gether doubtful — at all events I have never been able to recognize any granular matter 

 between pairs of bundles, as would be the case if they belonged to the latter type. A small 

 amount of granular matter is seen at the surface, and a number of fine fleecy processes 

 having an irregular disposition*, though I can say nothing more definite concerning them. 



If we now inquire as to the use of these transverse muscular prolongations so prevalent 

 in the Nematoids, I think we shall have no difficulty in answering the question. Sup- 

 posing the four sets of fibres to contract at the same time, they must necessarily tend to 

 diminish the calibre of the cavity of the body, and so exert a compressing force upon 

 the intestinal canal, tending to urge its contents in a definite direction according to the 

 order of their contraction. And seeing that no muscular fibres have been detected in 

 the intestinal canal itself, except at its two extremities, this seems to be the function 

 which they are destined to perform. 



Many anatomists have spoken of the existence of circular muscular fibres external to 

 the longitudinal. I have not only utterly failed to recognize the existence of such, but 

 am also quite at a loss to know what possible use they could subserve even were they 

 present — situated as they would be on the one side within a firm chitinous cylinder, 

 practically incapable of being contracted, and on the other external to the very strong 

 muscular envelope formed by the great longitudinal bands. 



Dr. Schneider believes the muscles of the Trichocephali do not conform in the tj-pe 

 of their formation either to that of the Colomyarice or the Platymyarice^, though as 

 regards the structure actually existing in Trichocephalus dispar, his views are at variance 

 with those of Ebebth. The latter believes that the muscles are lined internally with 

 a layer of nucleated cells much resembling pavement epithelium, and seems dis- 

 posed to doubt the organic continuity of these cells with the subjacent muscle tissue;]:. 

 Schneider, on the contrary, speaks of the muscles being covered by a homogeneous layer 



* Other fleecy processes having much the same appearance extend across the body, from lateral line to 

 lateral line, diverging in their course to encircle the alimentary canal, and so suspend it in the axis of the cavity 

 of the body (Plate XXVII. fig. 4). 



t Keich. and Du Bois-Eetm. Archiv, 1863, S. 20. J Untersuch. iiber Nemat. 1863, S. 49. 



