DENDY—REPORT ON THE CALCAREOUS SPONGES 7 
The length (or height) of the specimen is 31 mm. and the maximum breadth about 
14mm. The thickness of the wall of the sac near the broad end (made up chiefly of the 
radial tubes) is usually about 2 mm., but very variable. ( 
The texture of the whole sponge is delicate and fragile, and the colour in alcohol pure 
white. 
Owing to the bad state of preservation it is impossible to determine the distribution 
of the collared cells, but it is probable that they occur on the inner surface of the gastral 
membrane as well as in the radial tubes. The canal system makes a close approach to 
that of Dendya tripodifera, differing chiefly in the fact that the radial tubes are much 
less regularly arranged, while their blind outer ends, lying at very various levels, do not 
form an approximately even surface to the sponge, as they do in the Australian species. 
The radial tubes appear first as minute hollow buds, growing outwards from the thin 
wall of the central gastral cavity (gastral membrane). Such buds occur not only in the 
neighbourhood of the osculum but also on the lower parts of the sponge wall between the 
bunches of more fully developed radial tubes. They may be quite solitary but are usually 
linked together in irregular networks. I have not been able to determine how this 
“linked” arrangement of the young radial chambers originates. Their appearance, when 
the sponge-wall is viewed from the outside, suggests that they arise from one another by 
budding, like yeast-cells. Probably some grow out directly from the wall of the central 
gastral cavity and then give rise to others by budding. When fully grown the tubes are 
arranged in bushily branched bunches (Plate 3, fig. 4), the smaller ones coming off from 
the larger ones and the largest only (i.e. the main stems of the bunches) opening direct 
into the central gastral cavity. These main stems usually measure about 0°3 mm. in 
diameter. heir branches become much narrower and closely crowded together, their walls 
actually fusing where they come in contact with one another, but without lateral com- 
munication of their gastral cavities. Different bunches of tubes, on the other hand, 
remain to a large extent separate from one another. The openings of the main tubes of 
the bunches are very conspicuous on the inner surface of the gastral membrane, usually 
arranged in small groups and varying very much in size (Plate 1, fig. 4). 
Sometimes a group of chambers forms an irregular, rounded nodule, attached by a 
narrow stalk to the gastral membrane, and perfectly independent of its neighbours on all 
sides. One such nodule measures as much as 4 mm. in diameter, and the opening of its 
hollow stem into the gastral cavity, oval in outline, measures no less than 1°5 mm. in 
longer diameter. Usually, however, the openings in the wall of the gastral cavity are 
much smaller than this. . 
The prosopyles cannot be distinguished. They probably occur both in the gastral 
membrane and in the walls of the radial tubes. 
The skeleton consists of triradiates and quadriradiates ; I have found no oxea. The 
spicules all lie tangentially in the thin walls of the radial tubes or in the gastral membrane, 
and when an apical ray is developed it projects as usual into the gastral cavity or one of 
its outgrowths. In the gastral membrane (wall of the central cavity), as in the walls 
of the radial tubes, the spicules may be said to form a single layer, but their rays overlap 
one another copiously. Their arrangement is nowhere very regular, but in the gastral 
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