132 THE SPONGES. 



On comparing the different specimens, and making some use of hypoth- 

 esis, it becomes possible to describe the habitus of the species in the 

 following way. The sponge has differentiated upper and lower surfaces- 

 Primarily solid, in the course of growth it develops lobes, which may 

 spread and fuse, not only in the horizontal plane, but in planes above and 

 below the level of the original body. Thus spaces are partially enclosed 

 which continue to pass through the body in various planes. The enclosed 

 spaces may be small or large, and thus the whole mass comparatively 

 compact or very cavernous. If the growth be predominantly in the 

 horizontal plane, a flattened plate-like body results. When the growth 

 is not predominantly in one plane, a labyrinthine mass of anastomosing 

 lobes results. 



Except in shape, the several specimens agree. The color is a light 

 ashy gray. The sponge is firm, only very slightly compressible, and of 

 a marked cartilaginous consistency. 



The upper surface is in general roughened with closely set minute 

 projections which vary a good deal in character. In regions (part of 

 Fig. 1, Plate 18), the projections are fittingly designated as villi, and 

 consist of small tufts of more or less radially disposed spicules, a tuft 

 including only 2 or 3 spicules. Round the base of such tufts the sponge 

 tissue forms an elevation, and thus the projection is strictly conical, although 

 very slender. Such villi are exceedingly abundant over parts of the 



surface, especially in the peripheral region of the sponge. The villi 



intergrade with the larger elevations with which the greater part of the 

 surface is thickly covered, and which reach 1 mm. in height. These 

 elevations, which may be referred to as conuli, taper toward the apex. 

 In their distal portions at any rate, they are supported by the larger dermal 

 tufts of spicules, and (hence) frequently appear branched. In places the 

 conuli are especially low and feebly developed, such regions being almost 

 smooth. 



The under surface, as compared with the upper, appears in general 

 smooth to the eye and the touch, noticeable villi or conuli appearing only 

 here and there. 



Fairly numerous round oscula, 1.5 to 2 mm. in diameter, are scattered 

 over the upper and outer surfaces. They lead into deep main canals, and 



are especially developed on the prominences. To the eye the dermal 



membrane of both surfaces appears imperforate and opaque. In the 



