NATURE OF THE DRACUNCULUS, OR GUINEAWORM. 109 
right angle, leaving diamond-shaped spaces between the points of intersection, and con- 
"stituting a system of spirals in opposite directions round the body of the worm (Pl. XXI. 
fig. 10). 
These linear markings preserve a nearly uniform distance from one another, and pursue 
a straight course, without dividing or communicating in any way, similar to those of the 
external portion. And there is this in common with the three sets, that the lines, 
whether longitudinal or oblique, of the several superimposed lamellz do not correspond 
in position ; so that when those of the most superficial lamelle are in focus, there may be 
seen generally about nine fainter lines of deeper lamelle shining through, and closely 
filling, what would otherwise be each clear interlinear space (Pl. XXI. fig. 9). 
This appearance is very deceptive, and gives each set of lamelle the aspect of a single 
striated or fibrous membrane, as I, for some time, believed them to be, until on examining 
one of these supposed membranes with a high power, I discovered that a portion of a 
very delicate lamella had been torn off from those subjacent, leaving a toothed edge. 
The linear markings of this superficial lamella could be traced distinetly up to the torn 
edge; and in this situation also the lines of the uncovered portion of the subjacent layer 
were plainly visible, corresponding with a portion of the interval between the lines of the 
lamella above (Pl. XXI. figs. 11, 12). This I have frequently seen since; and the obser- 
vation evidently affords the key to the arrangement of these markings generally: and 
the fact is most important, as showing that this anomalous appearance of fibrous mem- 
branes in the integuments of these worms is a mere optical delusion, and that the 
membranes have no real existence, but that instead there exists a series of delicate and 
successively excreted chitinous lamellæ, having linear markings in definite directions— 
an arrangement fully in harmony with what we know of other analogous structures. 
The two internal sets of lamelle may be readily isolated by tearing a small piece of 
integument to pieces with needles; but the external set with the longitudinal markings is 
very difficult to separate from the outer portion of the integument, to which it is intimately 
adherent. These longitudinal lines are not so rectilinear as the oblique, and they are all 
rather difficult of detection, requiring a high power to distinguish those of the superficial 
lamellae plainly from those of the lamellae beneath. In this respect they are very dif- 
ferent from the transverse markings of the outer half of the integument,—the greater 
distinctness of these being apparently due to the fact that the alteration in texture, on 
Which the markings depend, extends through the whole thickness of this outer portion, 
whereas the lines which have a similar direction in each of the three sets of lamellz do 
not correspond in position, and, being produced by an alteration in the texture of one 
delicate lamella only, are necessarily very faint. 
There seems to be some slight difference, too, between the texture of this thick outer 
portion and the internal lamella, since its torn edge is generally even, whilst that of the 
lamellæ is always sharply jagged and toothed. 
The structure of the integuments of Ascaris lumbricoides and of A. mystax corre- 
sponds, in its general nature, with that of the Guineaworm just described, though it 
differs in several minor and unimportant details. The markings of all the layers are 
much more rectilinear and distinct in both these worms. They possess an external coat 
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