A SIEVE-LIKE MEMBRANE IN LEUCOSOLENIA. 267 
add that neither in the living nor preserved condition could I 
observe any trace of the flagella described by von Lendenfeld 
as present in all calcareous sponges (‘ Descriptive Catalogue of 
Sponges in the Australian Museum,’ Introduction, p. vi), and 
for my part I feel very sceptical as to their existence. 
A few words in conclusion as to the mode of life of this 
sponge. I have only found it between tide-marks in rock 
pools. So delicate a creature appears to shelter itself from 
the violence of the waves by creeping down in amongst the 
stems of the calcareous alge, &c. I have frequently pulled up 
a colony of Styela and found a rich ramification of the sponge 
tubes round the bases of the Ascidians. Hence it is a very 
inconspicuous form, and one may look into a pool full of it 
without observing any until one pulls up and examines the 
seaweeds closely. In one pool I found it specially abundant. 
This was a pothole about a foot and a half acress, and about 
two feet deep; the side towards the sea was concave and over- 
hanging, the other sides more or less straight, but all round 
there was a thick growth of weeds. Here, well sheltered from 
the waves which must beat over the spot four times in the 
twenty-four hours, the sponge attained the greatest develop- 
ment I have seen. Nearly every bit of weed was clothed with 
it, while under the overhanging seaward edge the sponge came 
out, as it were, from the seaweeds and formed the large masses 
mentioned at the commencement of this paper.! This pool 
Metschnikoff had before him a young and undifferentiated form of the ecto- 
derm. It would be of great- interest to trace the modifications of the 
ectoderm during the growth of a single form. 
1 In Sorrento my friend Dr. Otto Maas and I observed a very similar 
pothole at the entrance to one of the grottes, situated just at the water’s 
edge where the waves were constantly beating into it. This pothole also had 
the side towards the sea deeply concave, and what made it specially interesting 
was the fact that under the overhanging edge were growing a large number 
of specimens of a calcareous sponge (probably Sycandra raphanus; at 
any rate a Sycon) of various sizes, while the other sides of the pool were bare, 
except for a few weeds. Dr. Maas has observed, in his valuable paper on the 
development of Spongilla (‘ Zeitschr. f. wiss. Zool.,’? Bd. 1, 1890), that the 
larvee avoid the light ; and other sponge embryologists have observed the same 
thing so often, that one is justified, I think, in putting down this habit of 
