OF TILE NEMATOIDS, PAEASITIC AND FREE. 549 



open and the longitudinal muscles have been stripped off, at first sight there appears 

 nothing more than a mere granular layer situated on the external chitinous integu- 

 ment, the granules themselves consisting of rather large, highly refractive particles. 

 But a more careful inspection reveals a number of larger ovoid or spherical cells about 

 Tito" ill diameter, and provided with a distinct nucleus (Plate XXII. figs. 13 & 14) 

 scattered amongst the granules; and indeed it seems highly probable that most of 

 this gi-anular matter is either now contained in cells, or may be considered as the 

 remains of cell formation*. 



A very few fibres appear to interlace amongst this material, though these are almost 

 wholly collected into two distinct layers, the fibres in which have different directions, 

 and are aggregated together so as to form a loose mesh work or fibrous membrane. The 

 external and thinner of the two connects the cellulo-granular layer veith the chitinous 

 envelope, "and its very delicate fibres have a transverse direction; whilst the internal 

 membrane, made up of stronger fibres having for the most part a longitudinal direction, 

 serves as an aponeui'osis for the firm attachment of the great longitudinal muscles, and 

 in the intermuscular intervals it constitutes the bounding membrane of the lateral and 

 median lines. 



The chitinous lamellae are plainly divisible into five distinct primary layers, the most 

 internal of which is the thinnest, and presents very faint, close-set, longitudinal markings 

 (Plate XXIII. figs. 5, e, & 15). It seems rather more adherent to the enderon than to 

 the next chitinous layer, and is often removed with the former when the integument is 

 torn with needles. 1 have found nothing answering to this layer in Bracunculus. The 

 next two layers are much thicker, though equal to one another, and similar in all respects, 

 save that their oblique markings are in opposite directions (Plate XXIII. figs. 5, d, c, 

 & 14). These layers can be split into a variable number of lamellae, though not nearly 

 with so much facility as the similar layers in the Guineaworm, which in this latter animal 

 have also a greater proportional thickness. The markings (of the two layers) appear as 

 bright lines whose directions intersect one another, at very acute angles, in different 

 planes. The next layer, which is the thickest of aU (Plate XXIII, fig. 5, b), seems abso- 

 lutely homogeneous and without markings of any kind. This I have never been able 

 to isolate from the adjoining layers, though it and the others, with their respective pro- 

 portions, may be readily seen in thin transverse sections of a dried animal made with a 

 sharp razor and subsequently mounted in acetic acidf . Examined with the polariscope and 

 a selenite plate, the whole structure becomes still more distinct — the contiguous layers 



• Ebbrth (TJntersuch. iiber Nemat. p. 46) seems to have recognized this structure as composed of delicate 

 ceUs in the Trichocephalidoe, though ho speaks of it as beneath the skin instead of forming one of its most im- 

 portant layers: he sajs, " Dieht unter der Haut trifft man eine zarte feinkornige Sehicht, die mir aus sehr 

 zarten Zellen zu bestchen schcint." 



t After making sections of the Nematoids, whether fresh or dry, I always place them in acetic acid previous 

 to examination ; it not only renders them more transparent, but, owing to the rapid imbibition of the fluid, it 

 is the best means of restoring the circular form of the section. If the specimen is to be preserved, it should be 

 soon taken out of the acetic acid and mounted in glycerine. 



