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DE. J. S. BOWEEBANK ON THE ANATOMY 
The expando-ternate spicula, which are situated at the distal extremities of the radial 
fasciculi of the skeleton, diverge slightly from each other from their basal extremities, 
so that their triradiate heads, when firmly cemented to the inner surface of the ovarian 
stratum, form a strong and regular siliceous network, the points of the radii of each 
being cemented by keratode to those of its next neighbour ; and within the area of each 
of these meshes of the network there is the proximal end of an intermarginal ca-sity, 
the diaphragm of which frequently occupies the greater portion of the area, having a 
much greater diameter than that of the proximal orifice of the cavity, so that when 
fully opened its orifice is quite equal to that of the intermarginal cavity. The ovaries 
^'ary considerably in size in different species. In the adult and prolific condition they 
have the form of a strong, thick-shelled, more or less globose ovarium, having a funnel- 
shaped orifice at the apex, which communicates with the central cavity, which, in the 
prolific state, is filled with closely-packed minute vesicular bodies, very similar in 
appearance to those contained in the ovaria of the Spongilladse, but apparently more 
minute. In this condition of the ovary its parietes are formed of acutely cuneiform 
spicula, firmly cemented together by siliceous matter, the united apices forming the 
inner surface of the ovarium, while the united truncate bases form the external sur- 
face. In the early and immature state of the ovaria these truncated bases are not 
produced, and the young ovary has its outer surface bristling with pointed spicula, which 
are most acute in the youngest specimens, and become gradually more obtuse as they 
approach maturity. After the prolific contents of the adult ovary have been liberated, 
the internal cavity is gradually filled up by the extension inwards of the apices of the 
cuneiform spicula, until it becomes eventually a solid body ; and a similar secretion of 
siliceous matter is also frequently continued at the outer surface until it often assumes 
an irregular tuberous and quite abnormal appearance. 
The ovarian stratum of the crustular dermis is principally composed of exhausted solid 
ovaria ; but occasionally near the outer surface of the stratum a few prolific ones may be 
observed, but the greater number of these bodies and of those in an early stage of deve- 
lopment are situated amid the deeply-seated portions of the sponge, scattered irregularly 
over the sarcodous membranes and deeply immersed in the sarcode. In the young state 
they each appear to be surrounded by a firm stratum of sarcode, which, from its perfectly 
smooth and circular form, is apparently contained within a proper membrane, but in the 
fully developed and in the exhausted ovaria this sarcodous envelope is not observable. 
This description of the organization of the genus will apply equally well to any one of 
the seven species with which I am acquainted, and also to the nearly allied genus 
Pachymatisma, excepting the mode of the arrangement of the skeleton in the latter. 
Both the type specimens of Geodia in the Museum at the Jardin des Plantes appear 
to have had large central cavities ; but I have not found similar excavations in other 
species of the genus, excepting in one instance, a Geodia from Port Elliot, Australia; 
the internal surface in each of the three cases presents precisely the same appearance — 
a simple irregularly matted surface of spicula and membranes without any thickening of 
