24 
Proceedings of the Royal Society of Edinburgh. [Sess. 
attenuated to a fine point, though often it was broken abruptly; the 
opposite end was sometimes broken, at others it terminated in a very 
minute knob (scarcely visible to the naked eye), which, when magnified, was 
seen to be the rounded end of the basal spicule from which four hook- 
like processes equal in length arose ; they were recurved in their direction, 
almost parallel to the long axis of the spicule, and formed an anchor-like 
arrangement which assisted in fixing the sponge in the mud (figure). 
A close examination of the tufts showed that a number of the spicules, 
more especially near the proximal part of the tuft, had attached to them 
globular blackish specks, 300 to 320 ju in diameter, which contrasted in 
colour with the white spicules. Under low magnification they looked like 
very minute grains, and had with strong transmitted light a greyish-blue 
Anclior-like end of basal spicule of siliceous sponge, South Shetland. 
tint. Neither Canada balsam nor treatment with acetic acid and glycerine 
made the centre translucent, but the thinner periphery permitted greyish - 
blue-tinted siliceous microscopic flakes or scales to be seen, which, when 
superimposed on each other, gave opacity to the object. Owing to their 
hardness and brittleness, attempts failed to make sections through them. 
They seemed to be aggregations of siliceous plates attached to the spicule, 
the purport of which was difficult to explain. 
A brown substance was occasionally seen to surround some of the basal 
spicules in the proximal part of the tuft. The largest example was 6 mm. 
long and was fusiform. From its structure it was essentially a fragment 
of the body of the sponge which had adhered to the basal spicules. In 
part it contained nuclear-looking bodies embedded in a granular protoplasm, 
but a number of ray-like spicules were also present. Many of these were 
four-rayed tetracts, which radiated horizontally from a common centre, and 
the largest specimens measured 0*5 mm. between the tips of opposite rays. 
