1911—12.] Structure and Affinities of Branchiomaldane vincenti. 65 
ing tube. In the mid- ventral region the epidermis is thickened and highly 
glandular. 
The coelom resembles, in its relations and proportions, that of an 
ecaudate Arenicola. The coelomic fluid contains, besides the genital 
products described below (p. 67), numerous oval and spindle-shaped cells. 
Septa are present, as in Arenicola, at the anterior end of the first, third, 
and fourth segments. There are no septal pouches. The second and third 
septa are rather thicker and more muscular than those of specimens of 
Arenicola of the same size. Septa are also present at segmental intervals 
throughout the gill region. The muscles of the body- wall are arranged 
similarly to those of Arenicola : beneath the epidermis is a thin layer of 
circular muscles and the longitudinal muscle-bands (fig. 5). Oblique muscles 
occur in the segments posterior to the third septum, but have not been 
observed in front of this septum. 
The alimentary canal (fig. 3) is of the same type as that of 
Arenicola. The mouth, which is situated antero-ventrally in the 
peristomium, is either a transverse slit or a narrow crescentic opening. It 
leads into the pharynx, which is muscular, protrusible, and well provided 
with blood-vessels. The oesophagus is slightly dilated posteriorly, and bears 
there two elongate, conical, or ovoid glands, the walls of which are simple, 
that is, do not present infoldings, to increase the secreting surface, such as 
occur in the corresponding glands of Arenicola. The two glands have a 
common stalk, and a single opening into the oesophagus. The “ stomach,” 
which has thick glandular walls, on the coelomic face of which are 
numerous intersecting blood-streams, extends through nine or ten seg- 
ments, and then merges into the intestine, which opens at the terminal 
anus. The gut contains fine debris, in which fragments of sponge -spicules, 
and the frustules of several species of diatoms, are the only recognisable 
remains of organisms. 
The vascular system has not been studied in detail, as only preserved 
material has been available ; but, so far as ascertained, the arrangement of 
the vessels appears to be similar to that in an ecaudate Arenicola. Satis- 
factory evidence of the presence of paired hearts is not obtainable from 
the sections available, but observations on the living animal would be 
necessary to determine definitely the absence of these organs. The 
efferent vessels of the sixteenth and succeeding segments open into the 
dorsal vessel, so that, as in the ecaudate species of Arenicola , all the gills 
return blood to this trunk. The ventral vessel is enveloped with chloro- 
gogen cells. Many of the vessels of the branchial region attain a large size. 
The blood is red, due to the presence of haemoglobin. 
VOL. XXXII. 
5 
