IQI9Q. | N. ANNANDALE: Sponges, Hydrozoa and Polyzoa. 95 
zoarium may also be produced and in the mature colony the 
orientation of the zooecia is often radial, mainly in four directions. 
In any case a large number of the zooecia always point in the 
same direction. The colony as a whole is quite flat, the gelatin- 
ous ectocyst filling in the interstices between the zooecia. 
The individual zooecia maintain their identity distinct, but 
their ectocvst is so thick that their openings have in more conges- 
ted parts of the colony a honeycomb-like appearance. The ectocyst 
is, as already stated, usually quite hyaline and colourless, but it is 
sometimes darkened towards the distal extremity of the zooecia 
It is hard and almost cartilaginous for the greater part of its 
length, but the harder region ends abruptly near the aperture, 
which is surrounded by a thin, soft, mainly retractile membrane. 
The margin of the former region is well-defined, of an oval form 
and somewhat oblique in its long axis, which is mainly vertical in 
direction. Sometimes the external surface is covered with minute 
algae. The zooecia: are long, but somewhat variable in length, 
sometimes bent or curved in their long axis. They are distinctly 
flattened. Their transverse diameter (internal) is about 0°5 mm. 
and even when quite young they are of almost equal calibre 
throughout their length. Their long axis is parallel to the surface 
to which they are attached. 
This description applies to the normal zooecia which consti- 
tute the greater part of the colony, but in old zoaria zooecia of 
another type are produced at or near the terminal points of the 
branches. These are variable in shape and sometimes shorter, 
occasionally longer, than the normal zooecia. Zooecia of this type 
(which are only produced when the vegetative period of growth 
nears its end) never contain a fully developed polypide but only 
one or more statoblasts partly embedded in a strand of undifferen- 
tiated tissue, which broadens out towards the distal extremity of 
the zooecium. 
The polypide is much like that of H. punctata and offers no 
particular diagnostic characters. The tentacles are moderately 
short and not very numerous and the whole body is almost 
colourless. 
The free statoblasts are very like those of H. punctata, but 
not so variable in shape, a little more rhomboidal, and with a 
broader ring of air-cells at the extremities. The fixed statoblasts 
are large, broadly oval, of a dark brown colour and densely 
punctured on the surface. Each is, however, surrounded by an 
amorphous mass of dark horny material that obscures its true shape 
and ornamentation. ‘The statoblasts are not very numerous. 
Measurements of statoblasts (in millimetres). 
Free. Fixed. 
Length .. ae). 0°357-0° 374 0°459-0°561 
Breadth 2. 0°255-0°272 0°425-0°459 
Type-specimen. P. %, Z.S.1. (Ind. Mus.). 
