POLYCHAT LARVA. 593 
The peristomial segment bears a single pair of tentacular 
cirri; the second segment bears two pairs and a tuft of 
setae; and the remaining five segments bear uniramous 
chaetigerous parapodia, the first pair of these with a 
minute ventral, but no dorsal cirrus, and the rest with 
both a small dorsal and a small ventral cirrus. <A pair of 
almost spherical anal styles develop at about the same 
time as these parapodia, and also the two pairs of cephalic 
tentacles, which appear close to the anterior end of the 
prostomium (as seen in Pl. II., fig. 7, of the nectochaeta 
stage) as extremely transparent conical outgrowths, about 
40u long. 
The akrotroch with its unpaired “hook” is still 
present, its lateral extensions reaching very nearly to the 
cephalic tentacles. Two pairs of eyes are now present, 
one pair being smaller and slightly behind and on the 
inner side of the other, and embedded somewhat deeply - 
in the tissues. The neurotroch and telotroch disappear 
before the end of the metatrochophore stage; but inter- 
paratrochal cilia appear—first on the ventral surface in 
tufts (10 long), one below the base of each parapodium, 
and finally as complete amphitrochs (cilia 50 long). 
_ The prototroch is still at the height of its development, 
and consists of an anterior row of short and a posterior 
row of long cilia. At the end of the metatrochophore 
stage the larva is 500” long by 250” broad; behind the 
seven primary segments an unsegmented region occupies 
about one-tenth of the entire length of the larva. 
Nectochaeta.—tThe chief external changes that 
appear to take place during the remainder of the pelagic 
life of the larva are the development of additional 
seements from the anterior end of the anal unsegmented 
region, and the disappearance—shortly after this process 
has begun—of the akrotroch and oral cilia. Internally 
