POLYCH HT LARVA. 623 
has already lost a number of its provisional ones, though 
none of the other segments appear to have lost any of 
theirs. 
In an older larva (2,000”; 23 segments) the 
specialised setae of the fifth segment are much more 
conspicuous and project slightly, almost all the 
provisional setae having been shed from this, and from 
the first, second, and third segments. The tentacles are 
much longer and appear to arise nearer the middle line 
than in the younger specimen. In addition to this, the 
parapodia of the seventh and succeeding segments each 
bear a short (30) dorsal outgrowth—the rudiment of 
the gill 
crotchet has appeared. The lateral extensions of the first 
and amonest their ventral setae a single hooded 
three or four median ramified patches of pigment are 
now emphasised by a considerable reduction of the other 
parts, and the lateral patches are in some instances 
extended for a short distance on the ventral surface. 
The four most recently formed segments are pigmented 
on the same plan as segments 3-5, the lines of pigment, 
however, ramifying somewhat over the segments. The 
five pharyngeal pouches described in detail by Salensky 
(Bull. Imp. Acad. Sci., Moscow, 1908) reach the height of 
their development at about this stage. 
In the oldest specimen seen (25 segments) these 
pouches are disappearing again; the special setae of the 
fifth segment project as shown in Pl. IL, fig. 30. I have 
been unable to identify them with those of any adult 
form. ‘The shedding of the provisional setae has not 
progressed so far as in the previous specimen: In both 
these larvae, and in all others of sufficient age a number 
of segments, increasing with the growth of the body and 
commencing with segment 9, contains a deeply staining 
granular substance, which, in balsam preparations of 
Ss 
