46 
THE VOYAGE OF H.M.S. CHALLENGER. 
of the same size. Usually there are three internal longitudinal bars on each side. The 
stigmata are of moderate size and regularly placed ; there are usually three in a mesh. 
The Dorsal Lamina is a plain membrane. 
The Tentacles are eight in number, four long and four short, placed alternately. 
The Dorsal Tubercle is a small ovate aperture with prominent edges placed in the 
middle of the dorsal part of the prebranchial zone. There is a shallow peritubercular area. 
Locality. — Station 212, January 30, 1875 ; lat. 6° 54' N., long. 122° IS' E. ; depth, 
10 fathoms; bottom, sand. 
Two colonies of this species were obtained near the Philippine Islands from a 
depth of 10 fathoms. The dimensions of the larger colony are given in the above 
description. Those of the smaller one are : — length about 3 cm., breadth about 2 ’5 cm., 
thickness 1 to 3 mm. 
The colour varies considerably in different parts of the colony (see PI. I. fig. 4). 
The free edges formed by test only are a transparent light grey marked with more 
opaque ashy grey spots where the terminal knobs of the vessels are present. The 
anterior ends of the Ascidiozooids are almost white, but quite opaque. The circular, open, 
branchial apertures are clearly visible to the eye. The remainder of the colony is darker, 
and is in some places of a purplish-brown colour, while in others it has a slight bluish 
tinge. The colour is due to the pigmented cells in the mantle around the lower parts 
of the Ascidiozooids, and in the swollen ends of the vessels in the test. 
The colonies of this species are of such very considerable thickness ^ (see PI. I. 
fig. 4) that at first glance they are liable to be taken for a Sarcobotrylloides, but, on 
cutting into the colony, it is found that it is not a solid mass, but merely a comparatively 
thin layer incrusting a core formed of sand-grains, shell fragments, and Annelid tubes. 
The Ascidiozooids, in their arrangement, form the long winding rows characteristic 
of Botrylloides, and these rows, in some parts of the colony, bound comparatively large 
(such as 7 mm. by 5 mm.) elliptical or quadrate spaces free from Ascidiozooids and 
formed of test richly provided in its surface layer with brown-coloured terminal 
knobs of vessels. A similar arrangement is found in colonies of Botrylloides gascoi, 
Della Valle, from the Bay of Naples. The last species, however, differs entirely in 
colour and other particulars from the one under consideration. 
Under a strong lens or a low power of the microscope (l inch) the anterior part of 
the endostyle, the peripharyngeal band and the nervous mass are readily seen around 
the open branchial apertures. The terminal knobs of the vessels also form a conspicuous 
feature in such a surface view of the colony. They surround the Ascidiozooids on all 
sides (PI. I. fig. 5), and give the colony a variegated appearance on account of some 
' The measurements of the thickness given in the description are not the total thickness of the mass, including 
the sand and other foreign bodies, hut merely the distance from the upper to the lower surface of the test as seen in a 
vertical section. 
