550 DB. H. CHAELTON BASTIAN ON THE ANATOMY AND PHYSIOLOGY 



being accurately distinguished by bright and contrasting bands of colour. The external 

 layer, like the last, does not seem capable of being split into thinner lamella;, and though 

 not so thick as this, is thicker than either of the others. It presents well-marked, broad, 

 double contoured transverse lines (Plate XXIII. fig. 13). These are about rsVij" apart, 

 and mostly preserve a considerable parallelism with one another, except where it is dis- 

 turbed by the bifurcation or commencement of one of the lines, as shown in the figure. 

 They do not all therefore form perfect circles round the body, and differ from the corre- 

 sponding markings in the Guineaworm by their altogether more regular arrangement 

 and the greater number of these bifurcations*. 



Whatever the nature of the alteration in the chitinous substance may be, giving rise 

 to these markings, it seems to extend through the whole thickness of this outermost 

 layer, and is doubtless a change similar to that causing the markings, not only of the 

 other layers, but also of the chitinous lamellge in the Nematoids generally. This change 

 causes an alteration in the refractive power of the lamella ; and in some instances, at least, 

 I think there is evidence to show that this is due merely to an alteration in the thickness 

 of the membrane, as seems certainly to be the case with the irregular markings of the 

 integument in Prosthecosacter inflexus. In transverse section the lines are seen to cor- 

 respond to actual ridges of the integument (Plate XXVII. figs. 4 & 5). In other cases, 

 however, it may perhaps depend upon a mere alteration in density of the lamella in the 

 situation of the lines, or even upon a diminution in thickness. The number and arrange- 

 ment of the chitinous layers, and also the character of their markings, varies somewhat 

 even in the different species of the genus Ascaris, and to a considerable extent in the 

 Nematoids generally. The markings of the external layer, however, seem to afford a pretty 

 constant generic character. In Ascaris mystax, where I have looked for it particularly, 

 I have been unable to recognize the thin inner layer with the longitudinal markings. 

 In transverse sections of the integument of A. marginata, a number of fine lines may be 

 seen radiating outwards from the inner layers (Plate XXVI. fig. 1) ; these are remarkably 

 numerous in this species, though they may be seen more distinctly owing to their increased 

 size (especially in the lateral regions) in A. lumbricoides and A. megalocephala, extending 

 from a slightly swollen base through the two outer layers. There seems to be no reason 

 to believe that they are tubular, and they may be mere connecting perforating fibres. 

 In A. spiculigera, in the intervals between the transverse surface lines, there are series of 

 short connecting markings at right angles to them (Plate XXVI. fig. 17) ; whilst in a 

 deeper layer, between the external one and those with oblique markings, are somewhat 

 diamond-shaped markings, arranged in transverse series, and the same distance apart as 

 the external circular linesf. In the genus Strongylus the most pronounced external 

 markings are longitudinal, though these are intersected by very delicate transverse ones. 



* These markings must not be confounded with the apparent circular markings seen by the naked eye, which 

 are due as it were to wrinkling of the integument, and between any two of which would be included from thirty 

 to seventy of the circular lines described above. 



t These are referred to by Dcjabdin as " des series assez regulieres de lacunes.'" — Loc. cit. p. 206. 



