110 H. CHARLTON BASTIAN ON THE STRUCTURE AND 
with circular or transverse lines, the same as in Filaria medinensis, but, unlike it, they 
have no series of lamelle with longitudinal markings, intervening between this outer 
coat and the lamelle with oblique markings. When seen superimposed, the oblique 
lines of these lamellze are found to intersect each other and the transverse lines of the 
outer coat at a very acute angle. Internal to this, in Ascaris lumbricoides, there is 
also what appears to be a single delicate lamella, with very faint and close longitudinal 
markings; but I have not been able to discover anything similar in 4. mystax. The 
lamella with the oblique markings do not seem so numerous in either of these species 
as in the Guineaworm, and the external portion constitutes about three-fourths, instead 
of one-half, of the whole thickness of the integument. The integuments of these worms 
also are not so favourable for examination as that of the Guineaworm, on account of 
the extreme difficulty in isolating their component parts. 
Muscular System.—This is composed of four powerful longitudinal muscles firmly 
attached to the inner integumental layer, two of which occupy the dorsal and two the 
ventral region. They are made up of non-striated muscular tissue. As the longitu- 
dinal fibres run along the convexity and the concavity of the tail respectively, and the 
intestinal tube will afterwards be seen to terminate in the midst of the fibres occupying 
the concavity, as first pointed out by Mr. Carter, we must look upon these as ventral, 
and those along the convexity as dorsal, whilst the curve of the tail is thus ascertained 
to be in the median longitudinal vertical plane of the body, having a direction from above 
downwards. 
Only two longitudinal muscles have been described by other observers; but I think a 
more careful examination, particularly of the anterior extremity of the worm, will show 
that there are in reality four of these muscles, as in many other of the Nematoidea, two 
being dorsal and two ventral. The origins of the four muscles completely surround the 
head with a thin layer of fibres, the boundaries of each being marked off by the four 
crucial lines (Pl. XXI. fig. 13). "The two dorsal, running close together for two or three 
inches, one on each side of the middle line, then become fused as it were into one 
great muscle—though a trace of the original division continues apparent throughout 
the whole length of the worm, and becomes again rather plainer towards the tail. 
The two ventral muscles are arranged in just the samie manner; so that a broad, 
lateral, intermuscular interval. is left on each side between the dorsal and ventral group, 
equal in breadth to one-sixth of the circumference of the body. The four muscles are all 
of nearly the same size, each being of just the same breadth as one of the lateral spaces 
(Pl. XXI. fig. 19). Each is composed of fasciculi of very fine fibres, about zosooth of an 
inch in diameter, whilst the breadth of the fasciculi themselves is about zğpth of an inch 
(Pl. XXI. fig. 24). Frequent interchange of fibres takes place between contiguous 
fascieuli (Pl. XXI. fig. 23). : 
The arrangement of the muscles and their fasciculi may be well seen in the series of 
transverse sections shown in Pl. XXI. figs. 13-21. | 
The four muscles, after leaving the head, soon acquire a perceptible thickness; and it 
— be seen that the adjacent borders of the two dorsal and two ventral muscles respec- 
tively are very thin, whilst each gradually increases in thickness towards its free border 
bounding the lateral spaces. The irregularity of the inner surface of the muscular bands, 
