EEPORT ON THE HEXACTINELLIDA. 263 



relation in reference to the skin, or from the connection between the second and the 

 main central canals, but also from the structure of the soft sponge body, and especially 

 from the form and disposition of the chamber layer, or more correctly of the system of 

 irregular diverticula from the memhrana reticularis. As in all Hyalonematidse the latter 

 extends in the parenchyma between afferent and efferent canal-system in such a way, 

 that the convexity of all the diverticula is directed outwards against the entering 

 stream of water, that is, against the afferent system of canals. Every longitudinal or 

 transverse section of the sponge body shows that the memhrana reticularis found in the 

 partition between the two systems is so disposed or manifoldly bent outwards, that the 

 convexity of each small protrusion is against the processes of those canals which lie under 

 the fine-meshed quadi-atic dermal network on the flat or slightly convex sides (PI, LIL 

 fig. 3). 



The canals below the dermal membrane, which extends in the form of the fine-meshed 

 quadratic network, represent wide subdermal spaces, and those penetrating inwards are 

 somewhat uniformly wide afferent canals which do not break up into branches, but form 

 an anastomosing labyrinth (PI. LIL fig. 1). 



Large supporting spicules are represented in the parenchjrma by a few medium-sized 

 oxyhexacts, and by numerous oxypentacts, some of them with very long rays. Long 

 uncinate spicules also occur (PL LL fig. 3), disposed in brush-like strands or groups, at 

 right angles to the skin, where the parenchymal canal-wall is inserted on the external 

 skin. Besides these, we note smaller spicules of the following types : — Firstly, small 

 oxyhexacts with slim rays of equal or diverse length, beset to a variable extent with 

 somewhat distant, straight or slightly curved spines, which are inserted either at right 

 angles or approximately so (PI. LL fig. 15; PI. LIL fig. 5); secondly, oxydiacts of a 

 similarly spinose character, and with four short, smooth, conical median rays or spines 

 intersecting at right angles, and representing the survival of the other four degenerate 

 rays of the hexacts (PI. LIL fig. 4); and thirdly, isolated short uncinates with smaU short 

 barbs (PI. LI. fig. 6). 



The dermal skeleton, which supports the fine-meshed quadratic lattice-work, consists 

 of very varied, strongly developed, hypodermal oxypentacts, with long smooth tangential 

 rays, which are often somewhat strongly curved at the base, though sometimes but 

 slightly developed, and which are apposed to one another to form the quacbatic lattice- 

 work, while the more or less long, straight, proximal tangential ray, extends to a variable 

 distance inwards, and often projects freely into the hypodermal canal (PI. LII. fig. 3). 

 Only where the internal wall of the canal is connected with the skin does the tangential 

 ray lie throughout its whole — often considerable — length in the parenchyma. On the 

 tangential strands of hypodermalia, and on the bands of the dermal network extending 

 between the former, autodermal pentact pinuli occur, usually disposed in rows. The four 

 thick and moderately long, externally spinose, terminally somewhat conical or rounded basal 



