176 
_ 
away clean. The base is massive, of uniform character, with- 
out spines and without ostia. The branching stems that arise 
from the base are roughly circular in section ; the parts nearer 
the base are thicker than those more remote. The thicker 
branches are about 10 mm. across (not including the spines) ; 
they have shorter spines than the more terminal branches, 
and fewer ostia ; the ostia are more abundant on one side than 
on the other. In the more terminal branches the width varies 
from 5 to 8mm., and the apertures are more uniformly dis- 
tributed. The distance from one branch to the next is about 
30 mm., but it may be as much as 55 mm., or as little as 17 mm. 
The cross-bars joing up adjacent branches of the colony 
which M’Intosh noticed in Cephalodiscus dodecalophus (** Chal- 
lenger’’ Reports, Cephalodiscus, 1887) are here a marked 
feature of the tubarium. One such bar is seen towards the 
left-hand upper corner of plate 1, and a thicker one at some 
distance above the centre of the plate. They are solid, and 
have few or no apertures; they measure from 4 to 8mm. 
across. They act either as tie-rods to prevent the several 
branches of the colony from breaking apart, or else as bridges 
for the polypides to pass along from branch to branch. A\l- 
though, on the whole, the polypides reside in the cavities of 
the tubarium, yet one must admit the existence of migrating 
polypides, otherwise it is impossible to explain the increase in 
the length of the branches of the tubarium, the production of 
lateral branches, and the formation of the cross-bars and the 
spine-like processes of the tubarium. Possibly the wandering 
polypides are in all cases young ones which have only recently 
severed their connection with the stolon of their parent, and 
have left the parental home and are in search of a suitable 
position in the colony in which to settle down and secrete 
protecting tubes of their own. 
When the cross-bars are at all thick, they include embedded 
in their midst one or more of the spines which happened to 
occur in the neighbourhood. In the transverse section shown 
in fig. 8, plate 3, it is evident, from the way in which the strata 
of test are disposed, that the spine a is the organic axis, and 
remained for some time the only embedded spine of the cross- - 
bar. Later, however, the spines 6 and c became entangled 
and buried, and still more recently the spine d. 
Although in the case of specimen 18551 Dr. Gilchrist states 
that a great many of the polypides fell out and collected at the 
bottom of the vessel when the colony was plunged into for- 
malin, a great many still remain in the tubes of the tubarium, 
and entangled among the spine-like processes (see plate 1). 
