POLYCH HT LARVA. 579 
Only the five primary segments are present, but of 
these the last three bear appendages, even in the younger 
specimen (sp. C); whilst im the other (sp. A: Pl. L, fig. 1) 
the first (peristomial) segment bears on each side a lobe 
representing its dorsal cirrus; the second bears two 
similar lobes, representing respectively the single ramus 
of the parapodium, and its dorsal cirrus; the third bears 
a similar rudimentary dorsal cirrus, but a distinct 
chaetigerous parapodial ramus; the fourth a still longer 
parapodium; and the fifth a parapodium somewhat 
shorter than that of the fourth segment. 
Nectochaeta.—tThis stage may be said to begin 
in the Syllidae with the development of the parapodia of 
the anterior secondary segments. During this develop- 
ment the ventral peristomial cirri appear, together with 
the ventral cirri of the anterior chaetigerous segments, 
the cephalic tentacles, and palps; whilst the dorsal 
peristomial cirri increase in length. 
The prototroch, in species A at least, is still used for 
swimming, whilst the parapodia are used for crawling 
whenever swimming is impeded. ‘The setae are very 
long, and can be almost entirely withdrawn into the para- 
podium. The prototroch is complete, and consists of two 
rows of cilia* (Pl. I., fig. 1); those of the anterior row are 
70 in length, those of the posterior 50”. The mouth is 
lined with shorter cilia, and an akrotroch—a tuft or row 
of cilia between the prototroch and the apical plate—is 
present in the form of a median ventral tuft of cilia 20” 
in length, situated just in front of the prototroch in the 
hollow between the umbrella and the apical region of the 
* I have since been able to distinguish in a Syllid Metatrochophore 
(? Syllid B) a row of very short cilia anterior to these, as in Polynoé. 
These two rows, therefore, correspond to the posterior two rows of 
equal cilia in Polynoé, which they further resemble in that one row 
is held directed forwards and the other backwards. This larva bore 
three pairs of eyespots and a tuft of akrotrochal cilia 20 u long, 
