POLYCHAT LARVA. 607 
(see figure). It is continued downwards, to end 
ventrally on each side on the lips that border the capacious 
“mouth.” The formation of these lips shows that it is 
not the mouth of the Trochophore, but is the external 
aperture of a vestibule from which the original mouth 
still opens into the oesophagus. ‘This structure, which 
further involves the modification of the ciliated bands on 
the head and anterior segments, appears to be 
characteristic of larvae of the Spionidae and Polydoridae. 
It is described for several of these larvae in another paper 
(Gravely, 1909). 
This larva resembles certain known larvae of Spzo— 
so closely as probably to be of the same genus—perhaps 
also of the same species as some. Of these larvae, one 
reared from the ova of S. fudiginosus is figured by 
Claparede and Mecznikow (1869: Pl. XII., fig. 1M; and 
Cambridge Natural History, Vol. Il., fig. 145B, p. 275) 
with its setae, which are not quite so inordinately long as 
in the Port Erin form, held as when swimming. In the 
larva of S. meczntkowianus, also figured by these authors, 
the gut is enormously swollen with food-yolk, the larva 
being at first carried about attached to the body of the 
mother. The larva of SS. seticornis described by 
Leschke (1903: pp. 122-3; Pl. VI., figs. 7-9) and the Spio 
larva described by Hicker are both very like the Port 
Erin form above described. 
Spionid A (“Claparéde’s unknown larval Spio’’) 
(Pl. IL. figs. 22-27).—A transparent, colourless larva, 
originally described by Claparéde (1863: pp. 77-80; PI. 
VI.) and subsequently—under the name quoted above— 
by McIntosh (1894: pp. 71-74; Pl. VIII., figs. 4-7), is 
very abundant in almost every tow-netting taken at Port 
Erin during July. Although I am able to describe a 
later stage in the development of this larva than either 
RR 
