No. 3-] DEVELOPMENT OF MARI.XE SPONGES. 32 1 



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 (PI. 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, P"ig. 61, is a section vertical to the 

 sponge surface, including two furrows, /..with the intervening 

 ridges, ;-. 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. PI. 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, sp.,m. which the higher magnifica- 

 tion permits the flagellated chambers to be shown. PL 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 



