ON THE VITALITY OF THE SPONGIAD. 125 
a half of close observation with the hope of detecting the act of the closing 
of the pores, I was rewarded for my patience by seeing that the clear tense 
rounded margin of one of them, which was black by the aberration of the rays 
of light passing through it, began to lose its distinctness, and at the same 
time it assumed an irregularly oval instead of a circular form. The margin 
melted away, as it were spreading gradually inward towards the centre, and 
this action continued until the orifice became entirely closed, and not the 
slightest mark remained to indicate the place a minute previously occupied 
by a fully expanded pore. When thus closed, the membrane presented pre- 
cisely the same irregularly granulated appearance that characterized the sur- 
rounding tissue. Two other pores in the immediate neighbourhood under- 
went precisely the same process in the course of less than a minute. 
October 19th.—At 9 p.m. I found the sponge in very languid action, and 
completely clear internally of molecules and indigo. The excurrent tube bear- 
ing the osculum had assumed a new aspect. In addition to the usual conical 
projection of membrane, the apex was dilated into the form of asupplementary, 
obtusely oval bladder, terminated by the usual osculum in a fully dilated 
condition (fig. 7). Through this orifice, in consequence of its favourable 
position, I could focus clearly, down to the body of the sponge, and had 
there been cilia lining the interior surface of the tube, I could not possibly, 
I think, have missed seeing them; but I failed in detecting the slightest in- 
dication of their presence : very few pores were open, and none of those which 
I had diagrammed carefully on the 16th, nor any of those which I had 
observed on the 18th. 
I continued to observe this and several other small specimens of Spongilla 
for several weeks, but as the results were with very little variation the same 
_ as those I have previously described, it is unnecessary to detail them. 
The observations on Spongilla, as regards the forcible and the languid 
exhalation, are in perfect accordance with my description of those actions in 
the marine sponge Hymeniacidon earuncula, recorded in my report “ On the 
Vital Powers of the Spongiadz,” published in the Reports of the British As- 
sociation for 1856, p. 438. The vigorous imbibition and ejection of the 
surrounding water is as strikingly indicative in the freshwater sponge as it 
was in the marine one, of the period of feeding ; while the languid action in 
either case distinctly marks the aérating process only, during which the 
digestion of the nutritive particles previously imbibed is gradually effected, 
and the effete matter partially ejected. In the performance of these instinct- 
ive acts, Spongilla possesses the same degree of control over these actions 
that I have described in my former report as existing in the marine sponge ; 
sometimes the rapid ejection of the excurrent stream in the Spongilla was 
suddenly brought to a conclusion, while at others there was a very gradual 
decline in the rapidity of the action until it assumed the degree of force that 
marks the excurrent streams of the breathing action only. 
The structure of the pores, and the perfectly plastic nature of the dermal 
_membrane, as exhibited in these observations, are very remarkable. The 
sensitiveness of the sponge to injury, the rapidity of the act of closing those 
organs, and the power they appear to possess of opening new ones to any 
extent and in any direction they please, attest an astonishing amount of vital 
energy in a membrane in which I have been unable to trace any indication 
of the existence of fibrous tissue. 
