POLYCH“#T LARVZS. 609 
in the dorsal tuft. Before long a similar stout seta 
appears in the dorsal tuft, and two may be present in the 
ventral one. The most anterior seements, however, seem 
to be without these stout setae. 
In a larva of about twenty segments (1,500 long) a 
pair of lobes, the rudiments of the tentacles, are clearly 
indicated at the sides of the head, and parapodia, slightly 
biramous, already project from the surface of the body, 
though more usually this occurs in larvae of about twenty- 
five segments. The tips of both lobes of the parapodia 
are faintly tinged with brown; and each of the masses 
of opaque yellow pigment above mentioned is now 
situated between the bases of the two lobes of a para- 
podium (Pl. II., fig. 27). The individual segments 
lengthen considerably at about this time, and the tissues 
lose the strikingly embryonic appearance that they have 
so far possessed, at all events after staining. ‘This is due 
in part, no doubt, to the disappearance from the gut of 
its (yolky ?) contents referred to above; only occasion- 
ally, however, has any food material from the exterior 
been seen to replace this substance. 
The head and anterior segments show, in an inten- 
sified form, the structures briefly noted above (p. 607) as 
characteristic of larvae of Spionidae and Polydoridae. 
There are no nototrochs; gastrotrochs, however, are 
present on every segment, but become smaller, and finally 
disappear towards the posterior unseemented region. The 
gastrotrochs of the first three segments are modified in 
connection with the special! characters of the head; those 
of the remaining segments consist on each side of an outer 
and middle row of 40m cilia, and an inner row of 15yp 
cilia; the inner rows of the two sides of one segment do 
not extend to the middle line, but are separated by a short 
gap, as are the other parts of the gastrotroch. There is a 
short median dorsal gap in the powerful telotroch. 
