SOME LITTORAL OLIGOCHATA OF THE CLYDE. 55 
proximal curve, thickest in the middle (v. fig. 10, a). In length, the setee vary consider- 
ably, from 045 to ‘072 mm.; the average is about ‘06 mm. ‘There is no constant 
difference between the lengths of ventral and lateral setee; nor between those of the 
anterior and posterior regions of the body, except that the average leneth of the posterior 
is perhaps a little less than that of the anterior sete. 
The setz also vary considerably in thickness, viz. from ‘006 mm. to ‘0045 mm. 
The sharpness of their points varies, probably to some extent at least with age; newly 
formed setze (in which the basal curved portion is not yet present) have sharp points, 
while in others they may be quite blunt, almost truncated. 
Many setz show a refractile, elongated, sometimes spindle-shaped body in their 
centre, about the middle of their length (in glycerin preparations); the appearance is 
possibly due to some separation of the component fibrils (fig. 10, a). The setee appear to 
be shed periodically ; there may occasionally be seen two newly forming setze with an old 
one, in the same bundle, and thus there is presented the appearance of three setae per 
bundle. 
The alimentary tract shows no demarcation into separate regions between the 
0 Ge 
b SS 
Fic. 10.—Setee of Hnchytraeus dubius: a, pointed ; b, blunt, 
with refractile appearance in its centre. 
pharynx in the second and third segments and the intestine, which begins suddenly in 
the fourteenth. The septal glands in segments iy. and v. are of moderate size, those in 
seoment vi. are large; the individual cells composing the glands are visible in the fresh 
state. There are no peptonephridia. Chloragogen cells begin in segment vii., or there 
may be a few in segment vi. ; they are comparatively few and discrete up to xi., absent 
in xii. and xiii., numerous and close-set from xiv. onwards till near the posterior end, 
where they are fewer, and finally absent. The cells are of large size, with prominent 
oil-drops; in sections they are tall, elongated vertically to the alimentary wall, and 
present numbers of vacuoles. The alimentary canal is attached by stout strands to the 
ventral body-wall in each segment. 
The dorsal vessel may begin in segment xiv., or at the posterior boundary of segment 
xi. ; it bifurcates in the prostomium. The ventral vessel is formed about the level of 
septum ? by the union of the two terminal branches of the dorsal vessel. There are 
four commissural loops in the anterior part of the body ; these are contained mostly in 
the third and fourth segments, but their exact position is not, apparently, always the 
same. The blood is red. 
The ante-septal portion of the nephridia is small; very fine cilia are attached to 
the rim of the funnel, and longer cilia beat down the lumen; the post-septal is of 
TRANS. ROY. SOC. EDIN., VOL. XLVIII. PART I. (NO. 2). 9 
