TUBARIUM OF CEPHALODISCUS NIGRESCENS. 23 
branches. These arise mainly from this upper surface, and where a young branch is 
being developed the apertures of those tubes on the relatively main branch that lie 
close around it are symmetrically disposed around its base, and have the lips on the 
edges of the tubes most remote from the axis of the new branch. 
The above generalisation holds good in the main, but in places one meets 
with a most irregular disposition of the apertures of the tubes, and a pair of tubes 
opening to the exterior within 10 mm. of one another may have their apertures 
facing one another, and yet have no trace of a developing branch between them. 
A secondary branch behaves in its development as a foreign organism. The 
polypides of the new branch, having begun to secrete their tubes at some small area 
of the surface, incommode the polypides of the main branch in their immediate 
vicinity, and cause them to distort their tubes so that the openings are well outside 
the area settled upon. If a young branch be roughly handled, it breaks off and 
leaves an irregular flat or concave scar composed of soft test only, none of the tubes of 
the secondary branch running into the main branch (fig. 5, a and 8, plate 3). Should 
any deserted tubes of the main branch open within the area upon which a new branch 
is growing, it is covered over with common test, and, unlike the inhabited tubes, is 
found in the scar (fig. 5, ¢). 
In a young branch there is a marked contrast hetween the new tubes of its base 
and the old tubes of the main branch opening around its base. The old tubes have 
longer, thicker, and browner lips. The common test of a young branch resembles 
that of the apex of an old branch in being softer than usual, paler, and more 
transparent, and in being composed of thicker strata. 
Until this species of Cephalodiscus shall have been studied in the living state it 
will be impossible to make any definite statement with regard to the mode of growth 
of the colony, but so far as one can judge from the material available, the deductions 
are as follows :—the fully-grown buds, after severing their connection from the parent 
stolon, emerge from the tube within which they have been growing, and wander over 
the surface of the branch. They are gregarious, and eight or ten of them collect 
either at the apex of the branch, or, in the case of an old branch, settle in a patch 
at some convenient spot on the surface and start producing a new branch. They 
secrete profusely a soft investment common to them all, within with each lives in a 
sharply bent or curved tubular cavity with a bulbous blind end. By the addition of 
numerous thin layers to the interior of the neck of the bulb the “tube” becomes 
differentiated from the “test.” These lining layers are continuous with the margin 
of the tube, where they are comparatively thick layers and resemble so many super- 
imposed rings. The mouth of the tube projects slightly above the general test, and 
has no lip. 
As younger polypides than these migrate to the apex of the new branch and 
secrete profusely, the polypides under consideration lengthen their tubes in an 
obliquely radial direction in order to avoid being covered in—incidentally developing 
