POLYCHAT LARVA. 603 
nine intertrochal segments; the secondary appendages are 
developing in regular series. The rudiments of a pair of 
tentacles can just be recognised in a pair of slightly 
projecting lobes at the sides of the head. Both the proto- 
troch and telotroch are still well developed, and the inter- 
trochal cilia between the lobes of the parapodia have been 
seen in a living eight-segment larva; the only nine- 
seement larva obtained was not examined alive, and so it 
is impossible to say whether they are present on it or not. 
The complete development of Nephthys from the 
Trochophore has been described by Fewkes (1885: pp. 
180-184; Pl. IV., figs. 1-12). He states that the mouth is 
situated, as in the larva of Polygordius, between an 
anterior and posterior ciliated band, the latter bearing 
shorter cilia than the former, but differing from that 
found in Polygordius in that it becomes indistinguishable 
from the anterior band laterally and dorsally. Leschke 
(1903: p. 131) has since proved this to be the case in a 
Kuropean species also. His posterior (post-oral) band is 
not present in the Port Erin larvae. Fewkes’ oldest 
specimens—ten chaetigerous seements—show the develop- 
ment first of one and then of the rudiments of a second 
pair of cephalic tentacles, whilst dorsal and ventral 
“cirri” appear on each of the parapodia. A telotroch is 
present from the trochophore stage onwards, disappearing 
only in the very oldest larvae. Claparede and Mecznikow 
soe eX EVE, fig. 3), Hacker (1896: Pl. IIL, fig. 0; 
and 1898: Pl. 1., fig. 4), Leschke (1903: Pl. VII., fig. 9) 
and McIntosh (1908: Pl. I., figs. 1-3) have also described 
Nephthys larvae. McIntosh’s larvae (pp. 14-16) at least 
seem likely to belong to the same species as do those found 
at Port Erin during July. 
