remarkable Species of Cliona. 57 
determining the path taken by the currents of water coursing 
through the canal-system of the organism—or, again, that they 
may perhaps serve to differentiate the sponge into separate 
individuals. In some instances, however, every aperture in a 
chamber seems to be provided with an imperforate form ot 
these diaphragms, so as to be completely sealed up from all 
means of communication with its neighbours. I say ‘‘seems,” 
since it is difficult to make this out with certainty, and I have 
some doubt on the matter. Admitting, however, that I have 
determined this point correctly, then the whole arrangement 
suggests that of the seed of the freshwater Spongilla; for in 
such a chamber we have a particle of the sponge more or less 
spherical in shape, completely surrounded on all sides by an 
enclosure, which, while chiefly consisting of the calcareous 
walls of the chamber, yet does, when these are incomplete, 
possess also a wall of spicules set at right angles to its surface, 
and thus very much resembles the arrangement of the amphi- 
disks about the seed-like body of Spongilla. We might have 
here, then, a case of physiological adaptation, the existence of 
the calcareous chamber-walls making possible an economy of 
spicules, and dispensing with the necessity of a complete spi- 
cular enclosure. Thus, when the sponge went into winter 
quarters, all that would be necessary would be the plugging 
up. of the apertures in its burrows; and on the return of more 
genial conditions the growth of these plugs into perforated 
cones and open tubes would provide for the egress of the 
reviving sponge. 
Plausible as this may appear at first sight, it will not, I 
think, bear a close investigation. In the first place Cl/ona has 
not yet been proved to produce “‘seed-like bodies;”’ and though 
this evidence is merely negative, it is yet of great weight, if 
we consider that in no marine sponge whatever have these 
structures been discovered, and that in Spongilla they are pro- 
bably due to the influence of extreme changes in climatal con- 
ditions, to which the marine sponges are not exposed. Again, 
had the diaphragms of a single chamber formed collectively 
parts of a single enclosure, one would expect to find the heads 
of their spicules all turned in one and the same way—that is 
to say, either outwards or inwards relatively to the chamber. 
This, however, is by no means the case; no rule is to be 
discovered in this respect. ake for instance Pl. I. fig. 3, 
where two of the diaphragms, a and 4, will be seen to have 
their surface of spicular heads turned towards the interior 
their respective chambers A and B, while a third, c, has it 
turned just the other way, or outwards towards the exterior. 
It may be said, however, that this diaphragm belongs more 
