﻿SPONGES.-HALLMANN. 



163 



or frond, throughout about one-half its circumference, pro- 

 duced outwards on one side so as to form a wide flange ; it 

 measures 150 mm. in height, 100 mm. in breadth and 10 to 15 

 mm. in thickness. The specimens from the New South Wales 

 coast — all of which, it should however be mentioned, were 

 derived from \ery shallow water — are almost invariably of ir- 

 regular growth owing to the proliferation in various ways of 

 the original or primary frond. In .spirits, the surface is even 

 and glabrous, the consistency firm, tough, compressible and 

 resilient, and the colour light greyish-brown. The rather 

 thick dermal membrane is semi-translu- 

 <ent and enables one to discern the out- A j \ 



lines of the more superficial exhalant / \ / \ 

 canals lying close beneath. These canals, 

 which occur on both sides of the sponge, 

 are roofed by little more than derma] 

 membrane only. They run upwards in a 

 slightly radiating fashion from the base 

 of the sponge usually to the margin, and 

 terminate in small oscula ^ to i mm. in 

 diameter. Their number increases bv 

 occasional branching as they ascend, so 

 that the distance separating them remains 

 about the same throughout. In the drv 

 state, the dermal membrane forms a 

 dense whitish incrustation, and through 

 shrinkage, often conforms more or less to 

 the inequalities beneath. The partitions 

 between the canals then appear on the 

 surface as faint ridges. Where the in- 

 crustation is more or less denuded the 

 surface presents the appearance shown in 



WMiitelegge's figure ;i the ridges are, Fig. 31-C iiicrus- 

 however, sometimes much more, some- ^'^"s var. arenacea. 

 times much less stronglv pronounced. Modifications of the 

 The texture is extremelv dense and com- opposite extremities of 



J ^, - . . . the oxea. 



pact, and the sponge when dr\- is par- 

 ticularly hard and tough. The main skeleton consists 

 ot stout sinuous ascending fibres, repeatedly branching 

 and anastomosing. There are no true connecting fibres, 

 although the intercrossing of the longitudinal fibres often 

 produces the appearance of such. The echinating acan- 

 thostyles are so densely crowded on the fibres that the 

 coring spicules are usually concealed from view, but 

 when discernible they prove to be chiefly acanthostyle.s. 



1 Whitelegpe— ioc. cit., pi. xi., fig. 14b. 



