1919. | N. ANNANDALE: Sponges, Hydvozoa and Polyzoa. 89 
The specimens from sta. 20 are from the lower surface of blocks 
of hard clay which had fallen into the lake from cliffs of that sub- 
stance. Their skeleton-spicules exhibit less variation and are as a 
tule shorter and relatively stouter than those from the stems of 
bulrushes. Their normal gemmule-spicules are also usually stouter 
and shorter with relatively larger rotules, but very long spicules of 
the same type occur occasionally. The whole sponge is so full of 
particles of clay that it is almost impossible to study the structure 
of the skeleton in detail, but it is certainly (doubtless for this 
Fie. 4.—Gemmules and gemmule-spicules of Ephydatia fluviatilis from the 
Hamun-i-Helmand. A = outer rotules of a specimen from a block of clay at the 
edge of the lake: highly magnified. B—=agemmule of a specimen from the stem 
of a bulrush as seen from above: X 20. 
reason) very lax and amorphous and the groups of small spicules 
characteristic of the other phase seem to be absent, though small 
amphioxi occur scattered in the parenchyma. ‘The colour is that 
of the clay. The gemmules are normal except that in some single 
birotulate spicules are, as it were, plastered on outside the normal 
single row in a vertical or slanting position. ‘They are held in 
position by an extension of the outer horny coat, which covers 
them completely. 
It is probable that there was a difference in the chemical com- 
position of the water from which these two sets of sponges came 
