388 Proceedings of the Royal Society 
ance, from the. arrangement of the fasciculi. In stating that the 
direction of the muscular fibres in such sections is radiated, some 
explanation is perhaps necessary, for, while the fasciculi of the 
dorsal and lateral regions point more or less in this way, the arrange- 
ment at the raphe is different, since the oblique bands, passing 
down at an acute angle, direct, in the contracted state, the fasci- 
culi upwards and outwards. They gradually become vertical, and 
then slant in the opposite direction, before leaving what may be 
termed the ventral region. A firm band, apparently of the limit- 
ing membrane of the hypoderm, proceeds from angle to angle at 
the raphe. 
From this coat, at somewhat regular intervals, pass a series of 
muscular bridles, each forming a kind of diaphragm (dissepiment). 
Most of the fibres have a vertical direction. The same arrange- 
ment is observed in the Nemerteans and in most of the Annelida. 
Such bundles, of course, are altogether independent of the charac- 
teristic oblique bands of muscular fibres which pass from the 
lateral dorsal region on each side to the raphe at the ventral edge. 
Anteriorly the latter bands form, in contraction, a curve on each 
side, with the convexity directed inwards, and they enclose a some- 
what elliptical portion of the great longitudinal layer, w r ith a few 
cells and granules. The oblique bands spring from the basement- 
membrane, and thus pass through the longitudinal layer, — an 
arrangement very well seen in front, where the bands are of great 
thickness. Posteriorly the comparative slenderness of the oblique 
muscles makes this subdivision of the longitudinal layer indistinct, 
but it is nevertheless present. In this region, also, the distance 
between the middle of the oblique band and the longitudinal coat 
is considerable, the space being filled with cellular tissue and a 
few fibres. 
It will thus be observed that the animal has a very complete 
muscular system, relatively of great power, for the execution of its 
remarkable boring propensities in sand and gravel. 
Digestive System . — The mouth opens in the preparations on the 
ventral surface, a short distance behind the tip of the snout, and 
has prominent lips. It leads into a richly ciliated digestive 
chamber, which runs to the posterior end of the body. No dental 
organs of any kind exist, the food apparently consisting of sand 
