372 DISCOVERY REPORTS 



The second specimen is even more convincing. This is more regularly discoid 

 (Fig. 56 c), 21 cm. high by 17 cm. across by 3 cm. thick at the centre. The margin is 

 entire throughout, with no sign of attachment, and the only inclusions are a few patches 

 of sand at the centre and a small pebble embedded in the lower third (Fig. 56 d). Some 

 hydroids are growing out from the surface of the sponge, and the direction in which they 

 are pointing suggests that the sponge floated vertically (as figured) with the portion 

 containing the pebble lowermost. 



The third specimen has much the same shape and size as the second, but is entirely 

 without large inclusions, shell or pebble. The margin is entire throughout, but at several 

 widely separated points on it there is a peculiar roughening of the surface, suggesting 

 incipient rooting processes, as though the sponge, although unattached, had at times 

 come to rest on the sea-floor sufliciently long for rooting processes to start growing. 



That there can be no question of these sponges having been erect, with their bases 

 permanently embedded in sand,^ can be proved from the following: 



(i) Although members of the species readily take up sand (see below) these specimens 

 are particularly free from it. 

 (ii) The tissues and skeleton are normal throughout the entire margin, 

 (iii) Flagellated chambers are present just beneath the surface throughout the margin. 

 (Had these sponges been embedded in sand, it is unlikely that the flagellated chambers 

 would have persisted in the submerged portions.) 



With regard to the first point, the ease with which individuals of Tedania teniii- 

 capitata will absorb sand grains is shown by the majority of the Discovery speci- 

 mens. In some cases, the inclusions are confined to the base, which was presumably 

 buried in the sand, but in most cases sand is found throughout the specimen (Fig. 56^). 

 Fig. 56 e shows a section of a flabellate specimen with a sandy base, and Fig. 56/ shows 

 an irregularly "table-shaped" sponge (spreading horizontally) with several "legs" 

 which were buried in the sand at the base. In view of this therefore it is improbable 

 that the margins of the discoid specimens could have been in contact with the "coarse 

 brown sand" of the sea-floor without showing some trace of its inclusion. 



It is noteworthy that both the discoid specimens, when immersed in 80 per cent, 

 alcohol, only just sink. That is to say, they will sink, but the slightest touch on the under 

 surface, when the specimens are standing erect, will cause them to rise in the spirit. This 

 feature is more strongly marked than in any other preserved sponge experimented with. 

 Since the specific gravity of sea water is greater than that of alcohol, it is reasonable to 

 suppose that these particular sponges would be unusually buoyant. 



Other examples of sponges which may have floated above the sea-floor may be easily 

 found. The young of Cinachyra barbata, Sollas, for example, are sub-spherical (cf. 

 Kirkpatrick, igo8, Plate ix, fig. 3), completely covered with a surface pile of spicules and 

 showing no sign of having been attached ; and the same may be said of adult specimens 

 up to 10 cm. in diameter. Many specimens of Thenea show no evident point of attach- 



1 Coarse brown sand formed the substratum at Sts. WS 222 and WS 96 where these sponges were found. 



