314 A MONOGRAPH OF THE AUSTRALIAN SPONGES, 



microscopic pores of the surface the water either enters cavities 

 which lie underneath the skin, the subdermal cavities (Carter) or 

 flows through small canals which join and form larger tubes. 



These tubes afterwards again give rise to smaller ones, which by- 

 continual ramification finally supply the greater part of the whole 

 Sponge. In no part of the Sponge this system of canals, through 

 which the water flows centripetally, is in direct connection with 

 those canals through which the water passes on to the oscular 

 tube. There is always a layer of ciliated chambers present in the 

 Sponge, which layer separates the ectodermal canal system which 

 brings the water to the ciliated chambers, from the canal system 

 which carries the water away from the chambers to the oscular 

 tube, these latter canals are coated with Entoderm. The layer of 

 ciliated chambers is mostly folded in a very complicated manner. 

 Originally it has always been of a simple sack-shape, from which 

 shape the complicated structure of the adult Sponge is derived. 

 (F. E. Schulze Plakinidse.) 



The Ectodermal water-supplying canals are to be compared with 

 trees which grow from the sub-dermal cavities or corresponding 

 parts. Also, the Entodermal drain-channels are tree-shaped. 



The narrow canals arising from the ciliated chambers unite to 

 form larger branches which again, like tributary streams, run 

 together, uniting to a main drain which opens into the oscular 

 tube or cloaca. Only in a few Sponges, particularly the Syconidee, 

 the canal system is simple and unbranched. The Asconida? 

 (Leucosolenia) possess no canal system. 



All the mains open into a tube very much wider than any of the 

 others, which stands vertical on the surface of the Sponge. This 

 Oscular tube is mostly very wide, always when expanded visible 

 to the naked eye. It can be compressed, and may under 

 circumstances be quite oblitered if the Sponge contracts very much. 

 (Lipostomie.) This Oscular tube opens on the surface of the 

 Sponge, with a simple, circular aperture. In the case of the 

 Sponge being cylindrical, or consisting of a lot of parallel cylinders, 

 there is nearly always an Osculum or opening of the Cloaca at the 

 terminal face of every cylinder. Complications of this simple 



