626 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
mount, that traces of the special modifications of the 
fifth segment can be distinguished in Polydora A. Thus 
the stage at which these structures appear may be much 
later than was the case in the larvae examined by 
Agassiz; and this variability has also been noted by 
Hacker (1898: p. 17) in connection with certain species 
described by him. Apart from the question of the fifth 
segment, however, Claparéde’s 17-segment larva is much 
more fully developed than even the most advanced of the 
Port Erin forms; and the one serious difficulty that I 
see in including it definitely in the genus Polydora 1s 
that all the segments appear to bear normal short 
permanent capillary setae, the fifth segment bearing just 
as large a tuft as the others. However, as in many species 
of Polydora, there is a small tuft of capillary setae on 
the fifth segment in addition to the special stout setae, I 
think it probable that these larvae really do beiong | 
to the genus Polydora, for they bear gastrotrochs on 
segments 5, 7, 10 (not regularly alternate) just as in both 
species of Port Erin Polydora larvae, and the stellate 
patches of dense black pigment appear to be found 
exclusively in Polydora larvae. All known larvae of 
Polydora (six distinct species) possess patches of dense 
black pigment, and in at least four of these (Agassiz’s 
larva of P. ciliata, loc. cit.; Andrews’ larva of 
P. commensalis, 1891; one species of Hicker’s Polydora 
larvae, 1898; and Polydora A of the present paper) they 
are large and ramified, as in Claparéde’s larvae, whilst 
in the remaining two species (one of Hicker’s species of 
Polydora larvae, 1898; and Polydora B of the present 
paper) they are small, unbranched, and less definite in 
outline and arrangement. 
Differences in the shape and arrangement of the 
large ramified pigment areas, and in the disposition of 
