NER1LLA AN ARCHIANNELID. 
401 
The last parapodium has no cirrus, retaining, however, the 
usual two bundles of chaetse. De Beauchamp states that in 
his specimens the last segment only bears one bundle of 
chaetae. 
All the chaetae are simple and needle-shaped, with distal ends 
tapering to a fine point (figs. 1, 4). They are firmly embedded, 
in bundles of about ten to sixteen, in a cushion of epidermal 
tissue, which can be moved by appropriate muscles attached 
to the inner surface of the body-wall (figs. 8, 15). Thus, 
although the chaetae are arranged in dorsal and ventral 
bundles, the parapodia are not divided into a noto- and a 
neuropodium as in most Polychaeta. But the parapodia 
resemble very closely those of Saccocirrus in general char- 
acter, without, however, being' so retractile. 
In the presence of chaetae in the parapodia of the first 
segment Nerilla differs, so far as I am aware, from all known 
Chaetopods. It maybe considered as primitive in this respect, 
since the absence of chaetae on this segment is probably due 
to a process of cephalisation, which can only be looked upon 
as secondary. 
The anus is dorsal to a triangular pygidial tail process 
bearing two long jointed anal cirri. These are similar to the 
other cirri just described, but rather stouter (figs. 1, 5, 20). 
Kows of glandular cells, secreting a sticky substance, are 
situated on the ventral surface of the pygidum and its 
posterior process (fig. 7). This region serves as an adhesive 
organ whereby the worm can fix itself on to some foreign 
object. 
The mouth is large, with a crescentic lip forming its 
posterior limit, and a less well-defined bilobed lip in front 
(fig. 3). Cilia spread over the ventral surface of the pros- 
tomium and over the front and lateral walls of the buccal 
cavity. A ventral ciliated tract extends along the whole 
length of the body from immediately behind the mouth to the 
tip of the caudal appendage (figs. 3, 9). It flattens out just 
behind the mouth and on the pygidium ; but along the rest of 
the trunk forms a definite deep groove easily seen in sections 
