182 HIRCINIA. 



indications of irregular rugae or gyriform protuberances are observed, which 

 are often arranged in transverse rows. The oscula are small, 0-5-l*5 millim. 

 wide, and confined to the inner surface of the cup-shaped sponge ; they are 

 larger and more numerous near the margin of the cup than further down. 



The colour of the living sponge is brownish pink. Dry specimens are grey 

 or white, according to the nature of the foreign bodies which form the stout 

 cortex on the surface. Dry skeletons are very hard and incompressible. 



The sheleton consists of knotty and irregular main fibres, 0-2 millim. thick, 

 which extend longitudinally upward from the base of attachment to the margin 

 of the cup. These fibres contain a continuous series of large sand-grains, and 

 appear, in fact, as a single column of large sand-grains cemented together by 

 spongin. The main fibres form two layers parallel to the surface of the cup, 

 which are equally distant from the surfaces and from each other, so that the 

 wall of the cup is divided by them into three distinct layers of nearly equal 

 thickness — an inner layer and t\vo superficial ones. From these main fibres 

 slender branches, 0*05 millim. thick, are given off at frequent intervals. Most of 

 these branches extend in an irregular plumose manner to the surface, and per- 

 vade the superficial layers on either side. In the cortical layer only very few 

 and distant branches are observed. The branches in the superficial layers form 

 a network with polygonal meshes 1-1 -5 millim. wide. Large sand-grains are 

 frequently observed in their joining points. The distal ramifications of these 

 fibres enter the sand-cortex on the surface, which is 0*5 millim. thick. The 

 filaments are hyaline and smooth, in the middle 0'002-0"0025 millim. thick. 

 The terminal knots are 0*004 millim. broad. The filaments are pretty abundant, 

 and appear uniformly distributed throughout the sponge ; they do not join to 

 form bundles to any large extent. 



The inhalant pores are 0-002 millim. wide, oval, and scattered over the 

 outer and inner surface of the cup-shaped sponge. They lead into slender 

 canals which penetrate the sand-cortex. These are much and irregularly 

 curved, wending their way through the dense mass of large sand-grains 

 which form the cortex. The subdermal cavities into which they lead are 

 represented by tangential canals, 0*l-0'3 millim. wide, with annular strictures 

 at frequent intervals, which are pervaded by numerous exceedingly fine mem- 

 branes. Small groups of such subdermal canals converge to give birth to 

 inhalant canal-stems, 0*3 millim. wide, which lead perpendicularly down from 

 the surface into the interior of the sponge. These inhalant canal-stems never 

 extend into the central askeletous layer of the sponge. Abundant slender 

 branch-canals arise from their sides and supply the whole of that portion of 

 the sponge which lies outside the main fibres. The ciliated chambers are 

 strictly confined to these layers, none being found in the central layer. The 

 ciliated chambers are 0-033 millim. wide, and provided with short special 

 efferent canals leading into the exhalant branches, which are mostly about 



