1903. ] COBLENTERATA FROM ZANZIBAR. 115 
confined to one plane (Pl. XIII. fig. 1). The main stem and the 
larger branches seem to have divided dichotomously with the pre- 
dominance of the most favoured branch. The terminal branches 
are mery, delicate, branches of 6 mm. in length gradually attenuating 
from 0:2 mm. to 0°1 mm. in diameter. Each terminal branch ends in 
a facultative growing point, and it appears probable that the growth 
is continuous. I have compared my specimens from Z anzibar 
with a beautifully preserved specimen of Ceratella fusca, for which 
the Manchester Museum is indebted to Prof. Spencer ; and I have 
noticed that the Australian species is much coarser in appearance, 
especially in the region of the terminal branches. I have seen 
nothing in the Zanzibar species corresponding to what Spencer 
calls “The growing ends of the smaller branches” in Ceratella 
fusca, which are flattened in a plane at right angles to that in 
which the general growth takes place and are entirely devoid of 
zooids. It is possible that the difference may be accounted for 
on the supposition that in Ceratella fusca the growth is seasonal 
or periodic. 
The branches of C. minima are invariably rounded. I have 
seen no evidence of a compression or flattening in any region. 
The surface is relatively smooth and free from any spines. The 
hydrophores are represented by very narrow ridges on the 
proximal border of the hydropores. The principal horny fibres, 
running longitudinally with a slightly spiral twist, may be clearly 
seen through the superficial ectoderm, and in the spirit-specimens 
give a ribbed appearance to the surface (Pl. XIII. fig. 2). 
The Zooids are numerous on the terminal branches, less 
numerous on the thicker branches, and very scarce on the main 
branches, as in Ceratella fusca. On the terminal branches they are 
arranged slightly to one side of the two lateral lines at intervals 
of about one millimetre opposite or alternate to one another. A. 
few zooids occur more irregularly distributed. 
On comparing such a terminal branch with one of Ceratella 
Jusca, it is at once apparent that in the Australian species the 
zooids are more numerous and much more irregularly distributed 
on all sides of the branch. Hach fully expanded zooid projects 
about 0°'7 mm. from the hydropore, and is about 0°14 mm. in 
diameter. It bears a variable number, but usually nine capitate 
tentacles, each about 0-1 mm. in length. 
No gonophores were found on any of the three specimens I 
have examined. The skeleton in the terminal branches consists 
of one or two main longitudinal horny rods supporting numerous 
looping and irregular bands, which maintain the eylindr ical form 
of the branch (PI. S00 fig. 3). 
In the larger branches the main longitudinal rods are more 
numerous, and, being chiefly superficial in position, give a slightly 
spiral, longitudinally striated or ribbed appearance to the surface, 
in this respect offering a marked contrast to Cerateila fusca. 
A series of sections thr ough a small branch shows that there is 
present a thin continuous coat of ectoderm covering the whole 
branch, as described and figured by Spencer in Ceratella fusca, 
8 * 
