191 
of the tube was at times comparatively large. The 
otoliths, consisting of quartz grains, were quivering and 
revolying rapidly all the time the living animals were 
under observation. This motion is probably due to the 
action of the cilia of the proximal part of the tube. 
The motion of the otoliths almost ceased when sea water 
which had been standing over chloroform was added. On 
the ventral side of the peristomium at its anterior edge is 
a crescentic or nearly semi-circular aperture—the mouth 
(fig. 58). 
Between the peristomium and the first chietigerous 
segment there is a segment which, im all the post-larval 
stages I have seen is achetous. Benham* and apparently 
also Ehlerst have found a small seta in this segment, but 
evidently this is a transitory seta which soon disappears 
leaving the segment achtous as it is in the adult. Both 
the peristomium and this achetous segment are rather 
smaller than the succeeding chetigerous segments and 
both are usually divided into two by a faint groove so 
that, as in the adult, the region between the prostomium 
and the first chetigerous segment is divided into four 
rings. In the third of these the cesophageal connectives 
unite. By comparing these post-larval stages with adults 
it is clearly seen that the first two rings of the latter belong 
to the peristomium and the next two to the first true body 
segment which has lost its setee and has become fused with 
the peristomium (cf. figs. 5 and 57). 
There are nineteen chetigerous segments, in each of 
which notopodial and neuropodial setze may be seen (fig. 
56). The notopodial setze are of two kinds. Some are 
* Journal Marine Biological Association, New Series, Vol. III., 
p. 49, 1893. 
+ Zur Kenntniss von Avenicola maria, L., Nachrichten von der 
Kénigl. Ges. der Wissenschaften, Gottingen, 1892. 
