Sponges from South Australia. 209 



appears to manifest a power of selection or preference in this 

 respect. 



With reference to the development of the keratose fibre in 

 the dermal membrane, it may be observed that this originates 

 chiefly in the conuli which are the growing terminations of 

 the main or vertical fibre of the sponge, from each of which it 

 extends outwards and downwards radiatingly, like the ropes 

 of a tent, so that, as the fibre diminishes in size by branching 

 and subdividing, the subdivisions not only become united 

 between themselves, but meet and become continuous with 

 the like from the neighbouring conuli, whereby an inter- 

 uniting fibrous reticulation is formed in the dermal sarcode 

 between the conuli, in whose interstices the pores are situated 

 and protected ; while the keratose fibre may be cored or not 

 with mineral elements, as already noticed. 



Again, what has been stated of the external parts of the 

 sponge applies ca j t. par. to the internal ones or parenchyma ; 

 for as the sponge grows by the addition of layers to its 

 circumference, that is radiatingly, so the surface of to-day 

 becomes part of the internal structure of to-morrow, and thus 

 somewhat modified it passes into a cancellated form, which is 

 the parenchyma ; that is to say, the fibrous skeleton, cored by 

 mineral material or not, becomes a solid mass of reticulation, 

 in which the interstices are tympanized by the still poriferous 

 sarcode (as may be seen in a dried specimen), and the cancel- 

 lated chambers thus completed. Lastly, the whole is traversed 

 by the branches of the excretory canal-systems. I use the 

 latter in the plural number, because generally every vent 

 indicates a system. 



Still another condition arises from the amount of keratine 

 developed, which may be entirely absent in the lowest forms 

 of the Psammonemata (for I must confine myself henceforth 

 to this order, as we are now more immediately concerned 

 with it), where the sarcode retains its delicate pristine nature; 

 or it may be diffused throughout the sarcode generally, so as 

 to give it a horny consistence, as if the sarcode itself had 

 passed into this state, which is better seen in the dry than in 

 the wet specimen, when it presents a light amber colour, 

 while it is all grey together in the wet one ; so in the pro- 

 duction of fibre the mineral element, that is the foreign objects, 

 may be held together by a mere film of keratine, while on 

 other occasions the investiture of keratine may not only exceed 

 the core of foreign objects in thickness, but assume the con- 

 sistence and toughness of horn ; then as regards colour, the 

 keratine, which is generally yellow and transparent like amber, 

 may in some species be as transparent and colourless as glass. 



