SEA-FISHERIES LABORATORY. 271 



of the tube was at times comparatively large. The 

 otoliths, consisting of quartz grains, were quivering and 

 revolving 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 chretigerous 

 segment there is a segment which, in all the post-larval 

 stages I have seen is achaetous. 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 achsetous as it is in the adult. Both 

 the peristomium and this acheetous segment are rather 

 smaller than the succeeding chsetigerous 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 chaetigerous segment is divided into four 

 rings. In the third of these the oesophageal 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 setre and has become fused with 

 the peristomium (cf. figs. 5 and 57). 



There are nineteen chretigerous segments, in each of 

 which notopodial and neuropodial seta 3 may be seen (fig. 

 56). The notopodial seta? are of two kinds. Some are 



* Journal Marine Biological Association, New Series, Vol. III., 

 p. 49, 1893. 



f Zur Kenntniss von Arenicola marina, L., Nachrichten von der 

 Konigl. Ges. der Wissenschaften, Gottingen, 1892. 



