6 A MONOGRAPH OF THE AUSTRALIAN SPONGES, 



measure O'Ol in diameter (fig. 4). These little pores, as also the 

 large inhalent vents below them, are liable to great alterations in 

 size and can be contracted, the little ones even closed by the 

 Sponge. 



Canal System. 



The Canal System is very peculiar and totally different from 

 that of Oscarella. It approaches tliat of Halisarca but appears 

 also much more complicated and highly developed than it is in that 

 Sponge. 



The outer skin (b. fig. 4) is divided from the interior part of 

 the sponge, from the zone of ciliated chambers by a broad sub- 

 dermal cavity, 0*15 mm., wide. This cavity is continuous. It is 

 traversed in all directions by a highly complicated network of fine 

 threads measuring 0-005 — 0-01 mm., in thickness (s. fig. 4). 

 These repeatedly ramified anastomosing threads are cylindrical and 

 between the joining points generally more or less straight. These 

 threads connect the skin and the body of the Sponge. They 

 appear to be contractile to a certain extent and by their contrac- 

 tion the subdermal cavity can be diminished in size locally. 



The zone of ciliated chambers is much folded, and does not reach 

 the subdermal cavity everywhere ; there are moreover, empty 

 spaces left between, which appear as inhalent canals (i., fig. 3, j., 

 fig. 4). These are of an irregular shape, somewhat conic, as they 

 ai'e invariably wider centrifugally than proximally. 



The ciliated chamhers are of a regular elongate, oval, cylindrical 

 shape. They are longer than in Aplysilla (1), and represent some- 

 what the radial tubes of the Syconidse or the ciliated chambers of 

 Euplectella (2). They measure 0-17 in length and are 1"03 mm. 

 wide (/!, fig. 4). They have inhalent pores only at the distal end 

 which touches a part of the inhalent canal system. These pores are 

 ariable in number, probably because the Sponge can close them at 

 option. Generally there seem to be from 3 — 5. As a look at fig. 4 



(1) R. V. Lendenfeld. Neue Aplysmidae, Zeitschrift fiir wissenschaftliche 

 Zoologie. Band XXXVIII., Seite 234. 



(2) F. E. Schidze. The soft parts of Euplectella aspergillum. Transac- 

 actions of the Royal Society of Edinburgh. Vol. XXIX., p. 661. Tab. A. 



