794 
DE. J. S. BOWEEBANK ON THE ANATOMY 
ties of the sponge, and they appear to open over the -whole of those portions of the 
ca-vities not in contact with the adjoining ones. 
In Pachymatisma Johnstonia, a British sponge closely allied to the genus Geodia, 
we find the dermal membrane perforated by innumerable pores, some as minute as 
Yo^th of an inch in diameter, while others attain the size of -g^th of an inch. They 
are nearly equidistant from each other, but without any order in their arrangement. 
Immediately beneath the dermal membrane there is a stratum of membranous structure 
and sarcode destitute of gemmules, and about equal in thickness to one-third of that of 
the whole of the dermal crust, the remaining two-thirds of which consist of a stratum 
of gemmules or ovaries closely packed together, but perforated at intervals by the inter- 
marginal cavities. Through the upper stratum, destitute of ovaries, a small canal passes 
from each pore to the nearest adjacent intermarginal cavity, so that there are a series of 
them at various angles, all concentrating their streams of inhaled fluid at the distal end 
of the cavity, which is gradually expanded in diameter to receive them. In these 
sponges therefore each mouth appears to be furnished with a separate oesophagus, if I 
may be allowed the term, connecting it with a stomach-like cavity common to a 
group of mouths above it — a system of organization strikingly in unison with that of 
the higher classes of animals. In some cases, as in Geodia MfAndrewii and Parrefti, 
Boweebank, ms., we find the pores systematically congregated in groups, as in 
Plate XXXII. fig. 4, which represents four groups from the latter species, and this 
congregation is accounted for by the peculiarities of the form and arrangement of the 
intermarginal cavities of that class of sponges. 
The porous organs are still further complicated in a specimen of a branched sponge 
from the East Indies, presented to me by my friend Mr. S. P. Peatt. This sponge, 
which is a single branch about a foot in length and 9 lines greatest diameter, has 
nearly the whole of its surface abundantly furnished with peculiar and highly orga- 
nized areas, as represented in Plate XXXV. fig. 3, each of which covers and protects 
a deeply depressed porous area, the depth of which in many cases rather exceeds its 
own diameter. The protective organ covering this depression is elaborately and beauti- 
fully constructed, very closely resembling, in many respects, the spiracula of Pytiscus 
marginalis and other similarly constructed insects. Each of the depressed areas of 
the sponge is furnished with ten semifollicular membranous cones, the whole of 
them being based on a common external marginal ring of dermal membrane, from 
which they are projected inward in the same plane as the dermal surface until 
their apices nearly meet in the centre of the inhalant area. The exterior surface of 
each cone is perfect and continuous from the marginal ring of membrane to its apex ; 
but on the interior surface it is only perfect for about half its length from its apex 
backwards, as if half of the basal portion of a conical bag had been cut away from the 
remainder. Eig. 5, Plate XXXV. represents the exterior half of one of these protective 
organs, and fig. 6 the semifollicular structure of their conical organs. The membranes 
of which they are constructed are abundantly furnished with tension spicula, which are 
