312 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



nonexistent — that is. the "whole membrane is uniformly porous, and 

 is not divided up into perforated areas and intervening aporous 

 tracts. When it sinks down, as in a dried sponge, on the underlying 

 ectosomal trabeculae, the effect of " pore areas " is produced, that 

 is the ectosomal trabeculae now constitute low and apparently 

 aporous ridges between Avhich lie depressed areas that are obviously 

 porous. But examination of surface preparations shows that there 

 are pores (presumably afferent on one surface, efferent on the other) 

 everywhere, both over the ridges and in the depressed areas. These 

 pores are about 40 [x in diameter, separated only by narrow bands 

 full of asters. They pierce the thin dermal membrane, opening into 

 the subdermal spaces which fill the ectochrote. 



The subdermal spaces open below into cylindrical endochonal 

 canals which pass radially through the sterrastral layer. These 

 canals are about 200 [x in diameter, and 1.5-2 mm. apart. 



The subdermal spaces doubtless represent the expanded and rami- 

 fied outer (ectochrotal) parts of independent cribriporal chone-canals, 

 such as occur in some species. It is a question, in this species, 

 whether these spaces are all continuous with one another, thus con- 

 stituting a single system, or whether the whole set of spaces is 

 divided, as in some forms described by Lendenfeld (1006, G. stel- 

 lata, etc.), into unit systems, each unit system representing the outer 

 part of a single chonal canal, which still connects at its center with 

 the inner (endochonal) part of the same canal. (See under Geodia.) 



The fact that the dermal membrane is everywhere perforated by 

 closely set pores speaks against the idea that the subdermal cavities 

 are grouped in unit systems, for if pores are everywhere, so must 

 be subdermal spaces. The subdermal spaces within the limits of 

 an ectosomal trabecula (see above) are doubtless very small. 



The shape and arrangement of the subdermal cavities can best 

 be directly studied in sections vertical to the surface, and in views 

 of the under surface of the ectochrote, when the latter is cut free 

 from the rest of the cortex. In sections they appear as rounded 

 spaces. In the flat preparations of the ectochrote they appear as 

 irregularly polygonal spaces, 175-500 jx in diameter, separated by 

 thin partitions 50-100 |x thick. In the partitions here and there 

 lie the radial skeletal bundles which as seen in this way are com- 

 monly 100-350 |x apart. There is no evidence of the grouping of 

 the subdermal cavities in unit systems. Nevertheless the specimen 

 is a dried one (although the drying was carefully carried out) and 

 this detail of anatomy can not therefore be definitely decided. 



The interior of the sponge wall is filled with very abundant huge 



(somal) oxeas, scattered in all directions, often in tracts. In the 



peripheral region of the choanosome ihis diffuse skeleton gives place 



to radially arranged megascleres grouped, though often vaguely, 



