20 THE SPONGES. 



figure, which represents the sponge after a part of the hiteral surface has 

 been sHced off. A ridge such as usually marks the passage of the upper 

 or o-astral into the lateral or dermal surface is distinguishable only on 

 one side of the body, and does not contain peculiar marginal diacts. The 

 gastral surface to one side of the deep cavity exhibits a sharp protuberance, 

 which superficially suggests the central conus found in some species of 

 Hyalonema. At another point (in the left of the figure) the periphery of 

 the body, where gastral and dermal surfaces meet, is pi-oduced into an 

 ear-like lobe overarching a lateral concavity. The expanded part of the 

 body has a greatest horizontal diameter of 24 mm., and a similar depth. 

 The peduncle, which is flattened, is 10 mm. thick in one transverse axis 

 and 5 mm. thick in the other. 



At one side of the stalk-like process, just beneath the surface, traces of 

 the bundle of root spicules remain. Three of the spicules are still in place. 

 These are broken across at their lower end, but may be followed upward in 

 the sponge as far as the union of the peduncle with the expanded part 

 of the body. In addition, seven cavities remain, from which root spicules 

 have been pulled out. These cavities are mostly 350 to 400 fx in diameter, 

 while the actually remaining spicules range in diameter from 75 to 200 [x. 



The entire body is very dense and firm, the canals being 0.5 mm. and 

 less in diameter. These small canals open in some abundance on both 

 dermal and gastral surfaces. The dermal and gastral membranes are not 

 reticulate, but exhibit where uninjured a thick furze of projecting pinuli, 

 which is discernible to the eye. 



The parenchymal macroscleres are smooth oxyhexacts and smooth 

 oxydiacts. In the oxyhexacts the rays are subequal and tapering. In 

 the commoner sizes the ray measures 420 x 24 /x to 1 mm. x 70 fx. The 

 spicule is only fairly abundant. The oxydiacts are exceedingly abun- 

 dant, scattered in all directions in the upper body, arranged predominantly 

 lengthwise in the stalk. There is commonly an enlargement, often very 

 slight, at or near the middle, and the rays taper evenly. The spicule 

 measures 1-2 mm. in length, 12-20 /x in thickness. 



The hypodermalia and hypogastralia are abundant and alike. They 

 are smooth oxypentacts with no remnant of the distal ray, the other rays 

 tapering evenly. The size varies considerably. In a common size the 

 tangential ray measures 370 /x x 36 /x, the proximal ray 670 /x x 40 /x, but 

 much smaller spicules are abundant. 



