ON THE VITALITY OF THE SPONGIAD&. 121 
ship be of good type and can be always fully loaded; but seeing that load- 
draught is limited by local circumstances and other considerations which may 
not limit the length and breadth, it becomes a matter of calculation to deter- 
mine at what point the admitted advantages of size become neutralized with 
reference to any particular service by the limitation of load-draught in pro- 
portion to beam. Let us have all the advantages we can get, without running 
into extremes, by which those advantages become sacrificed. 
are not public interests involved in this matter, and is it not a matter of 
grave importance, meriting the attention of the British Association? I beg 
to conclude with the suggestion, that it is only bystatistics that the deficiencies 
of our present maritime system can be properly searched into and brought 
to light; and it is only by the force of statistical exposition that the re- 
quired remedies can be devised. It is therefore respectfully submitted, that 
the constructive type of shipping as respects the proportions of length, breadth, 
and depth, constitutes a subject of inquiry which merits the notice of the 
Statistical Section of the British Association. 
Further Report on the Vitality of the Spongiade. 
By J. 8S. Bowersank, LL.D., F.R.S. &c. 
[With a Plate. ] 
In the Report on the Vitality of the Spongiade which I had the honour of 
_ reading to the Association at Cheltenham last year, I detailed a series of ob- 
servations on the inhalation through the pores and the exhalation of water 
through the oscula of a marine British sponge, Hymeniacidon caruncula, 
Bowerbank, MS., and I was enabled to determine with certainty the eapa- 
bility which that sponge possesses of opening and closing the oscula at its 
pleasure; but I could not in that series of observations satisfactorily deter- 
mine the nature and powers of the imbibing pores, as these organs can only 
be seen distinctly in operation in very young and transparent specimens. I 
therefore determined to confine my researches on this subject more especially 
to Spongilla fluviatilis, specimens of which may readily be obtained of small 
size and under very favourable circumstances for the observation of the 
_ porous system. On the 13th October, 1856, my friend Mr. H. Gilbertscn, 
of Hextrerd, brought me several young specimens of this species, one of which 
‘had attached itself to a watch-glass, in which it had been kept for observation. 
The point of attachment was a thin membrane projected from the edge of the 
sponge (a, fig. 1, Plate I.), having in it a few single spicula irregularly dis- 
posed, and with very little appearance of sarcode upon it ; and above the thin 
attached membrane there was a second one, which was a prolongation of the 
upper surface of the sponge. The body of the sponge was thin, concave at 
the upper and convex at the lower free surface. It was nearly circular in 
its outline, and rather exceeded half an inch in diameter. Atone portion of 
the margin it had been recently extending its dimensions, and the space in- 
tervening between the old surface and the new one had the appearance of 
being one large cavity, the new dermal membrane being forced outward and 
supported from the points of the radial lines of the spicula of the newly 
produced portion of the skeleton, the outer surface of the membrane curving 
q inward, from point to point, in a manner that plainly indicated the forcible 
