100 
AUSTRALASIAN ANTARCTIC EXPEDITION. 
Microscopical study of them, under varying conditions and from different 
aspects, reveals a new type of bristle ; new not only to this family but, as I think, new 
to the class. 
Some time previously I had made a drawing of one of the chaetae from a group 
separated out and freshly mounted in glycerine; it was symmetrical, finely pointed 
with a narrow flange on each side, and very similar to that figured by Fauvel (1897) 
for Ampharete grubei (pi. XVII, fig. 24.) But amongst them I found others in which 
the bristle is curved and has only one rather broader flange. I supposed therefore 
that there were two kinds of chaetae in the bundle. 
Some months later, when preparing this account for publication, I had occasion 
to refer to my preparations, one of which was in Canada Balsam. I was surprised to 
see that all the chaetae are alike, curved, with a single flange. Wishing to ascertain how 
I could have been deceived in my earlier examination, I cut off a fresh parapod, sep¬ 
arated out the chaetae and made a new mount in glycerine. 
Again I saw in most of the chaetae two narrow flanges. I then pressed the cover- 
slip so that the chaetae might be flattened out a little ; now all of them had a single 
flange. I then lifted the coverslip, turned the chaetae about and re-examined them. 
Again I saw several with the two flanges. 
A careful study under a high power informed me that the chaeta really has three 
flanges, two narrow ones lying in one plane, symmetrically arranged, and a third broader 
one in a plane at right angles to them ; and in this position the chaeta is curved. 
Having made this discovery, it was easy to detect the three flanges in some of the 
chaetae, and I have drawn one of them (fig-. 118-120). 
To what extent this observation may shed light on discrepancies in the accounts 
of chaetae in some families, e.g., the Terebellidae, I cannot say. It is evident that a 
renewed study of the bristles in certain families is desirable. 
The ventral surface of the thorax is nearly flat, and traversed by a wide shallow 
median furrow, which increases in depth posteriorly, and after the last gland shield 
becomes very deep but narrower; the margin of the furrow is formed by the rounded 
muscular ridge on each side. 
The uncinigerous neuropods commence below the 4th notopod. Those on the 
anterior segments of the thorax are vertical ridges, limited to the sides of the body, 
and originating near the hinder boundary of the segments; their edges rise only slightly 
above the surface. In the hinder segments each neuropod becomes more prominent, 
thick and fleshy, while in the abdomen they are narrower and become flap-like (fig. 
114). The neuropod is now a quadrangular flap directed backwards and outwards; 
its free edge carries the uncini. On its upper surface near the body wall is a small 
rounded papilliform upgrowth (which is, perhaps, a dorsal cirrus). By the 12th 
abdominal the neuropods are already much longer and project still further; the dorsal 
