POLYCHAT LARVA. 639 
that the paleae now project forwards as in the adult, and 
that the umbrella is much further reduced than in the 
earlier metamorphosis stage described above; in fact the 
creature bears a closer resemblance to the adult than to 
the larval form. A median tentacle 40, long has 
appeared at the anterior extremity of the prostomium— 
the apical pole of the larva. A little behind this on the 
ventral surface are a pair of laterally compressed. lobes 
(Pl. IV., fig. 45; L.); these are probably developed from 
the lobes above the mouth over which the prototroch 
extends in the previous larva; their identification is 
rendered a little uncertain however by the fact that in 
the present larva the prototroch, which was only visible 
during life, seemed to be situated immediately behind 
them. The cilia of the prototroch were no longer active— 
it is of course possible, though I think not probable, that 
this was entirely due to the length of time that the larva 
had been kept in confinement; the creature was quite 
active otherwise, and twisted backwards and forwards 
very vigorously. 
The lips, usually so conspicuous in the living larva, 
were not seen at all in this specimen. ‘The black pigment 
spots of the larva have disappeared completely from the 
prostomium, and to a considerable extent from the body 
as well (compare Pl. IV., figs. 42-44 with figs. 45-46). A 
pair of tentacles is present lateral to the paleae. Uncini 
are just distinguishable in the body-wall. The creature 
had not begun to construct its tube when. killed. 
Tube-secreting stage.—Several little 
worms in their tubes were taken at the surface, and one 
of these is shown in Pl. IV., fig. 46: ‘The pair of ventral - 
outgrowths of the head seen in the second of the 
metamorphosis stages described above are held, in fixed 
specimens, close against the body (Pl. IV., fig. 46; ZL.), 
but can be extended out from the body during life. 
ty 
