No. 3. ] DEVELOPMENT OF MARINE SPONGES. 321 
red color make it exceedingly conspicuous. The specimens 
found on the mangroves are generally more or less ovoid in 
shape, with two or three oscular papillae, an inch or two long, 
projecting from the upper surface. The surface is furrowed in 
the most intricate and irregular fashion (Pl. XIX, Fig. 60, shows 
a small portion of the surface). The furrows are generally very 
shallow, but are conspicuous both in fresh and alcoholic speci- 
mens, because the tissue here is gelatinous. In the depig- 
mented alcoholic specimens, the furrows look much darker 
than the ridges. The ridges, as will be seen in the figure, 
exhibit numerous rounded and slight elevations, which in places 
may appear as well-marked papillae. On the oscular papillae 
the furrows often become regularly arranged, when they pursue 
a comparatively straight course towards the end of the papilla, 
meeting one another at acute angles. At the end of each 
papilla there is usually a single osculum leading into a shallow 
cavity, into which open several large efferent canals. There 
may, however, be two or three oscula set close together on the 
end of the same papilla. 
The division of the sponge body into the interlacing net- 
work of dense and gelatinous tracts mentioned above is shown 
in any section. Pl. XIX, Fig. 61, is a section vertical to the 
sponge surface, including two furrows, f, with the intervening 
ridges, x, Both the superficial gelatinous tracts directly beneath 
the furrows, as well as the deeper ones, show in their centre 
one or more large canals (efferent canals). The dense tracts 
alone have the true sponge tissue, the gelatinous tracts con- 
taining no flagellated chambers. The difference between the 
two is made the more striking in that the dense or spongy 
tracts contain a close meshwork of spicules, which is absent in 
the gelatinous tracts. Pl. XIX, Fig. 64, is a small portion of 
such a section as Fig. 61 with skeleton omitted, and shows a 
part of a superficial gelatinous tract, g.,together with a part of 
the adjoining spongy tract, sf.,in which the higher magnifica- 
tion permits the flagellated chambers to be shown. PI. XIX, 
Fig. 62, is a section across the base of an oscular papilla with 
skeleton omitted, and shows the connection between a super- 
ficial gelatinous tract and a deep lying one. Like the network 
