POLYCHAT LARVA. 587 
By the end of the metatrochophore stage (PI. L, 
fig. 17) the appendages of the first eight segments have 
all assumed their final form. The parapodia project from 
the body-wall to a distance of 100” (exclusive of the 
setae), and the dorsal tuft of setae has made its appear- 
ance; the elytra are about 1o0u in diameter. ‘he para- 
podia of the ninth segment are developing: it is hard to 
determine whether this is a belated primary or precocious 
secondary segment, for although it appears only after the 
parapodia of the eight preceding segments have reached 
an advanced stage, yet it develops so rapidly that it soon 
reaches the same condition, and the parapodia of these 
nine segments alone function throughout the nectochaeta 
stage, towards the end only of which do any further 
segments begin to appear. 
Shortly before the end of the metatrochophore stage 
the neurotroch disappears. In preparation for the necto- 
chaeta stage each segment is slightly elongated, so that 
the parapodia are less closely crowded and can function 
as organs of progression. 
Nectochaeta.—tThe head has begun to lose its 
larval features: its breadth is considerably less than 
before; the prototroch gradually disappears; the akro- 
troch is reduced in extent and becomes extremely difficult 
to distinguish—it probably consists of a single pair of 
minute tufts of cilia situated on the ventral surface near 
the middle line, in the angle formed between the umbrella 
and the anterior part of the head. By the end of this 
stage these remnants of the akrotroch, the prototroch, the 
ciliated area round the mouth, and the cilia by the 
erescentic eyespot, have completely disappeared. The 
three cephalic tentacles and the palps can now be dis- 
tinctly seen projecting from the surface of the head—the 
lateral tentacles dorsally over the anterior, the palps 
