156 
THE VOYAGE OF H.M.S. CHALLENGEE. 
duct takes its beginning in the largest specimen at about 80 mm. behind the mouth. 
In aU the specimens examined by me, excepting the largest one dredged at Station 298, 
the alimentary canal sends out anteriorly a large diverticulum, which, in an individual 
160 mm. long, has a length of about 50 mm., and is situated about 50 mm. behind the 
water- vascular ring. It is held in a proper position by the mesentery to which it is 
attached. The cloacal dilatation of the intestine is considerable ; the respiratory-trees 
are well developed, and both its branches run out from a common base ; the left tree 
is shorter but more branched, its ramifications being in communication with the plexus 
of pseudhsemal vessels. The right tree attains almost the length of the body itself. 
At the base of these respiratory organs, a smaller bundle is often present. The 
longitudinal muscles are composed of two bands. 
In the specimens obtained at Station 298 the calcareous deposits are totally absent, 
probably owing to some impurity in the alcohol. In the specimen from Station 
299 some very fragmentary, irregular, three- or four-armed spicules are present, which 
commonly seem to bear an outwardly directed process, but I only found these deposits 
in the dorsal processes (PI. X. fig. 1), and they were evidently in a state of solution. 
The integument is soft, thin, and pliable. 
The specimen dredged at Station 299, measuring in length 235 mm. and in breadth 
about 70 mm., is much more macerated than those brought home from the other Station. 
I am by no means fully convinced of its identity with the latter specimens, but they present 
an obvious resemblance. Considering that the deposits are dissolved and the bodies them- 
selves are very deformed and macerated, it is impossible to decide whether they are 
representatives of the same species or not. The individual from Station 299 has the 
Polian vesicles much shorter, only 30 mm. long, and the two thin bundles of reproductive 
organs have the tubes narrow and slender and up to four times (or more) dichotomously 
branched. 
Having finished the above description founded on the specimens from Stations 298 
and 299, I obtained the forms brought home from Station 300, in consequence of which 
some additions are necessary. These specimens, kept in purer alcohol, are less macerated, 
and their colour is dark violet, sometimes almost black ; the middle part of the back 
commonly presents a lighter colour. The largest specimen measures in length slightly 
more than 300 mm., and its tentacles are nineteen. Though the calcareous ring is 
absent, the other deposits are not all spoiled. The general shape of the deposits of the 
perisome seems to be three-armed, with the ends of the arms slightly branched or pierced 
by a hole ; the centre of each such deposit carries a strong vertical column, the flattened 
and dilated end of which is provided with long spines or processes (PI. X. fig. 7). By 
reason of these closely placed spinous columns the surface of the perisome is rather rough. 
However, even in these specimens the greater part of the deposits of the body-wall is 
dissolved. Lately I have got four other specimens provided with twenty tentacles from 
