POLYCH ®T LARVA. 633 
first of the two bands of powerful cilia is present; but 
none of these early larvae have been examined alive at 
Port Erin. 
Further stages in the development of these larvae 
than that shown in Pl. IV., fig. 14, I was unable to 
follow. Béraneck (1894), however, has described the later 
stages of another species of Chaetopterus. The earliest 
stage observed by this author corresponds roughly to the 
latest stage described above, but differs from it in that 
the segments of the anterior body region (i.e., the part in 
front of the first mesotroch) are already indicated in the 
outlines of the body, but as yet bear no setae. Subse- 
quently the region in front of the anterior mesotroch is 
shown to give rise to the anterior region of the body, the 
segment between the two mesotrochs to the segment 
bearing the wing-like lateral processes, and the remainder 
to the rest of the middle and the whole of the posterior 
body-regions of the adult. 
The development of Chaetopterus from the ovum to 
the Trochophore has been fully worked out for 
Chaetopterus varropedatus, Ren. (pergamentaceus, Cuv.) by 
Wilson (1882). He notes the existence of a temporary 
mesotroch (anterior to and developed earlier than that 
retained in the latest trochophore stages), and imme- 
diately behind this a pair of lateral flagella, which also 
disappear during the trochophore stage; these temporary 
structures appear in the earliest Trochophores (one to five 
days), which show a ventral mouth of normal size leading 
through an oesophagus anteriorly to the stomach as in the 
Trochophores of less modified worms. Apical and anal 
tufts of long cilia are present, the latter being carried 
backwards on the end of the caudal appendage as this 
develops. 
Subsequently the mouth is enlarged and_ pushed 
