OF THE KEMATOIDS, PAEASITIC AND FEEE. 566 



of fine granular substance, having numerous interspersed clear spherical spaces or 

 " vacuoles," at the same time believing this substance to constitute an actual portion of 

 the muscle-cells, and to be in reality but another form of the " Marksubstanz." I am 

 inclined to think that Schneider's description is the more correct from what I have 

 seen in some of the free Netamoids, and more particularly so, as even Eberth, in the 

 same place, speaks of the resemblance of the muscles of these latter to those of the 

 Trichocephali. Thus in Symplocostoma longicollis I have seen a similar finely granular 

 material lying on the surface of the muscles containing in its substance what appear 

 to be bright spherical spaces (Plate XXVIII. fig. 132), since they have no defined 

 boundary wall*. This substance also exists in the form of a multitude of long-tailed 

 processes extending into the ca\ity of the body, each of which has a similar bright 

 space in its dilated free extremity. Whether, however, this is an independent layer 

 of glandular substance merely lying on the muscles and differing from the ordinary 

 " Marksubstanz," or medullary portion of the muscle-cells, I am unable to sayf . I 

 think it possibly may be so, since I have recognized the rudiments of a somewhat 

 similar granular layer (Plate XXIII. figs. 8 & 9, e) on the surface of the triangular 

 muscle-cells of A. lumbricoides^. And if this is really the case, we have only to suppose 

 the development of this substance to be extreme whilst that of the bladder portion of 

 the cell is in abeyance, to reconcile the type of muscle-formation in the Trichocephali, 

 and certain of the free species, with that of other Nematoids, since Eberth's observations 

 agree with my own as to the presence of fibrous processes (Fortsatzen) in the former 

 animals ; whilst with regard to the free Nematoids, the difficulties of the investigation are 

 such that we can only say that no such processes have yet been detected in them. The 

 animals are too small to enable satisfactory transverse sections of the requisite tenuity 

 to be made ; neither can their bodies be slit with more ease in a longitudinal direction. 



NEEVOUS SYSTEM. 



Most various and discordant have been the statements made from time to time con- 

 cerning the nervous system of the Nematoids ; some mistaking for it portions of the 

 integumentary, muscular, or even alimentary organs, whilst others have been unable 

 to recognize any traces of such a system in these animals. 



CirviER and Serres seemed to be of opinion that the Nematoids possessed two lateral 

 nerves, in all probability mistaking the lateral integumental bands for these ; whilst 



• I should, however, be inclined to look upon them as jelly-like masses of a transparent albuminous material 

 rather than actual vacuoles. 



t The structure which in the paper on the Guineaworm (he. cit.) I described and figured as a layer of tes- 

 sellated nucleated cells lying on the muscles in that region of the body compressed by the development of the 

 genital tube, I now believe to be actual parts of the muscle-cells similar to those figured in the present memoir 

 (Plate XXV. fig. 15), merely altered in appearance by the pressure to which they have been subjected, and 

 actually torn from the surface of the muscles by the scraping process necessary for their removal. 



t I had actually sketched such a structure before I was aware of these doubts concerning the Trichocephali 

 and free Nematoids. 



