800 
DE. J. S. BOWEEBANK ON THE ANATOMY 
obtain in all species. Thus, during the course of my investigations at Tenby, I observed 
that while, amidst the numerous specimens of Hymeniacidon caruncida and Halichondna 
^panicea that covered the rocks in the neighbourhood of St. Catherine’s Cave, the former 
rarely exhibited an open osculum in the absence of the water, those of the latter species 
were frequently more or less open. 
The most beautiful and striking view of the ditferences existing between vigorous 
action and the comparative repose of the breathing process is exhibited in Grantia 
ciliata. In this species the pores are situated on the obtusely conical distal terminations 
of the intermarginal cells or cavities, each of which is furnished with a long fringe of 
spicula surrounding its porous end, their proximal terminations being cemented, for 
about a third of their length, to the slightly curved surface of the base of the cone. In 
the state of the comparative repose of aerating inhalation, and when the base of the 
conical extremity of the cavity is not distended by the incurrent action, these spicula all 
converge to a point at the level of their own apices, and the water thus gently inhaled 
passes between the shafts of the spicula, forming the protective cone to the inhalant 
pores, and effectually preventing any extraneous matter from approaching them. But 
when the vigorous feeding action commences, the distention of the base of the conical 
portion of the cavity brings it into lines parallel to the axis of the cell, and thus the 
conical fringe of spicula assumes a cylindrical form, and the molecular food of the animal 
is freely admitted to the pores. 
A corresponding action obtains in the exhalant system of this interesting sponge. 
The mouth of the great central cloaca is furnished with a thick fringe of very long and 
slender spicula, which by the contraction of its sides near the mouth are all brought to 
assume a conical form like those appended to the inhalant cavities ; but when the inha- 
lant action is in vigorous operation, and the oscula are all pouring their streams into the 
cloaca, the force of the water thus accumulated distends the mouth of the cloaca to such 
an extent as to cause the fringe of long spicula to assume the form of an open cylinder, 
or in some cases it is expanded to such an extent as to become slightly funnel-shaped, and 
in this condition the fsecal stream may be seen issuing from it with considerable force. 
There are many other interesting points in the structure of this highly organized and 
interesting sponge which I will not advert to at length, but refer my reader to a fuller 
and more complete history of its structure published by me in the ‘ Transactions of the 
Microscopical Society of London ’ for 1859, vol. vii. p. 79, plate 5. 
Thus we find that inhalation is the primary vital operation mduced by ciliary action, 
and that exhalation is merely a mechanical effect arising from the primary cause. "We 
find also that these actions are separated into two distinct modes ; the one exceedmgly 
active and vigorous, exerted only at intervals and for short periods, and the other gentle 
and continuous. If we combine the consideration of these peculiarities of function with 
those of the anatomical studies, we find that the incurrent streams are always received 
in intermarginal cavities, and that these organs, however modified, are always present, 
and in some cases can be distinctly and strikingly separated from the great mass of the 
