124 Proceedings of the Royal Society 
being quite external to all the muscular layers, and covered only 
by the cuticle and hypoderm. In a line with the first bristles, the 
layers have assumed a more definite appearance. Beneath the 
hypoderm is a circular muscular coat, which, however, is somewhat 
irregular in its arrangement ; for, toward the dorsal region, the 
layer spreads out at each side, and the fibres mix with the oblique 
muscles of that part, while only a very thin layer stretches across 
the middle line of the dorsum. Within the former is a more or 
less developed longitudinal layer — best marked at the ventral aspect. 
A long oblique muscle extends from the lateral dorsal region on 
each side to the middle of the body-wall; and an important feature 
is the situation of the nerve-cord in close proximity to the inferior 
attachment of this muscle to the hypodermic basement-layer. 
Various muscular fasciculi, as before, attach the oesophagus to 
the body-wall, and the bristle-muscles and those of the lateral 
appendages have made their appearance. 
A little behind the foregoing it is noticed that the circular 
muscular layer is less continuous (though strong inferiorly), and 
that the longitudinal has been grouped by the other fibres into 
certain definite bands, the most conspicuous being a double dorsal 
and two lateral. The former fibres, indeed, have now assumed 
considerable bulk, a thin circular layer only intervening between 
them and the hypoderm. The formation of the lateral longitu- 
dinal muscles, again, is interesting on account of their homological 
bearings. From the inferior bristle-tuft, and from the region on 
each side of it, a strong series of muscular fibres converges toward 
the side of the oesophagus, and then splits into two bands. The 
outer bundle is the more powerful, and at the infero-lateral region 
of the body it bends somewhat sharply outward to be attached to 
the wall. The fibres thus arch over a chamber on each side for 
the lodgment of the ventral longitudinal muscle. In ordinary 
transverse sections they are much stronger than the other, and, 
moreover, have the nerve-cords at their insertion. The second 
series slants downward and inward, and is chiefly composed of fibres 
passing from the dorsal arch by the side of the oesophagus to 
mingle with the circular fibres at the ventral surface. A thin layer 
of longitudinal fibres also occurs on the internal aspect of the 
ventral transverse band (a part of the circular coat). 
