COLLECTED BY THE SCOTTISH NATIONAL ANTARCTIC EXPEDITION. 461 



The main skeleton is made up of a regular reticulation of fibres. The principal 

 fibres run upwards through the sponge. They pierce the dermal membrane and 

 project slightly above the surface. They are connected by short fibres running 

 only from one principal fibre to the next. The transverse fibres are at right 

 angles to the main ones, so that fairly regular rectangular meshes are formed. 

 The main fibres consist of closely packed oxea, multiserially arranged, and covered 

 by a distinct layer of spongin. They are usually from 0'04-0'08 mm. in diameter, 

 but sometimes rather thicker ones are to be seen. They vary in distance from each 

 other from about 0*l-0'35 mm., but for the most part they are about 0'2 mm. apart. 



The transverse fibres average 0'03 mm. in diameter. They consist of a distinct 

 sheath of spongin enclosing uni- to multiserially arranged oxea. There is no special 

 dermal skeleton. 



Spicules. — Oxea. — These are short, thick, slightly curved, and tapering to rather 

 short points. They are 0'115-0'13 mm. in length, and have a maximum diameter of 

 0'014 mm. Many slender, young oxea are to be seen in the fibres with the fully 

 developed spicules. 



One of the specimens, which is about 75 mm. by 30 mm. in diameter, and one 

 small fragment are interesting on account of the spicules, foreign to the species, 

 which are incorporated in a beautifully regular manner in the skeleton. Large 

 spicules were noticed projecting from parts of the free under surface of the sponge 

 over an area of several square centimetres, while the broken edge of the specimen 

 showed layers of different thicknesses parallel to the surface, which gave a stratified 

 effect to that part of the sponge. An examination of vertical sections showed that 

 the multiserially arranged oxea of the main fibres have in many parts been replaced 

 by the large styli of Polymastia littoralis n. sp. , a sponge taken at the same locality. 

 The main fibres are connected by single oxea, sheathed in spongin, so that a 

 beautiful ladder-like structure is formed, the oxea proper to the sponge being the 

 rungs and the large styli the sides of the ladder. Sometimes the main fibres contain, 

 instead, bundles of the small dermal subtylostyli or single large cortical tylostyli of 

 Polymastia. Occasionally the large styli are reinforced by a few oxea, or by small 

 subtylostyli, lying parallel to them. In places the arrangement is very irregular. 

 Sometimes a distinct sheath of spongin is seen covering a considerable part of the 

 large styli, which, however, do not seem ever to be completely enveloped in it. 

 Directly beneath the surface of the sponge numerous vertical bundles of the dermal 

 subtylostyli and numbers of large styli of Polymastia occur in the reticulation of 

 oxea proper to the sponge. The whole forms rather a dense layer of spicules. 

 Similar layers parallel to the surface are found at intervals through the sponge, 

 as if they marked stages in growth. They give a stratified appearance to the 

 structure of the sponge. The transverse fibres seem always to contain oxea. The 

 apices of the Polymastia spicules are directed towards the surface of the sponge. 

 The spicules are, as a rule, quite uninjured, and their axial canals are not wider than 



