1910.] AND INVERTEBRATES OF ST. HELENA. 129 



spiiit is black on the surface and whitish in section, but the black 

 colour is due to decomposition, for Mr. Cunningham reports that in 

 life specimens are buff-coloured with faint reddish-brown patches 

 on outstanding parts, and paler buff in section. The sponge is 

 rather tough but yet breakable, slightly compressible but inelastic, 

 and differing greatly in texture from the tough leathery C. reni- 

 formis. The surface varies in character, being smooth here and 

 there, but mostly irregular, deeply pitted, reticulate or tuber- 

 culated, the differences being due to the amount and kind of 

 foreign material. The numerous incurrent pores, which are all 

 closed and barely perceptible, are scattered over the surface. 

 They are visible, however, in thick clarified sections at the 

 beginnings of the incurrent canals. The oscules also are scattered 

 and flush with the surface. They occur mostly on the inner wall 

 of the cup. They vary in diameter from 2-8 mm., and are 

 provided with a membranous sphincter. 



The ectosome forms a very thin delicate skin, very different 

 from the tough thick cortex of C. reniformis. Worm tubes and 

 root-fibres and stems of Eudendrhim project above the surface or 

 may be skinned over by the ectosome. These and other foreign 

 bodies are abundant in the interior. 



The Canal System. — A slightly stained, well clarified thick 

 section presents a most striking appearance (PI. VII. fig. 5). The 

 fine initial incurrent canals pass in obliquely from the surface 

 pores and meet at various angles to form larger inhalants. These 

 systems of initial — they can hardly be called intra-cortical — - 

 canaliculi are not regularly arranged like the pore systems in 

 C. reniformis, but are irregularly dendritic (fig. 4). The larger 

 incurrent canals, as they ramify down into the sponge, are mapped 

 out very distinctly, owing to their having a wide tubular central 

 axis whence much finer canals radiate out at right angles. This 

 most remarkable arrangement may be compared in appearance 

 to the fine brushes used for cleaning test-tubes, only one 

 must imagine the brush to branch continually, and many of the 

 radiating bristles also. The end branches of the " bristle " canals 

 abut on the choanosomal mass. The terminal main axes of the 

 incurrent canals end in terminal tufts of branching " bristle " 

 canals. It is so unusual to find innumerable very fine canals 

 passing off at right angles from much wider canals, that at first 

 in thin sections of the sponge I mistook the " bristle " canals for 

 strands of connective tissue. The ends of the branching " bristle " 

 canals form the prosodi of the flagellated chambers. These 

 terminal canaliculi are so extremely fine and delicate as to be barely 

 perceptible at first, for they consist of a single layer of pavement 

 epithelium. Accordingly the canal system is diplodal (figs. 6, 7). 

 The existence of diplodal canal systems has been denied *, but the 

 photographs of sections of Corticium candelabrum, Chovdrilla 

 niccula, and Oscarella lobidaris published by Schulze clearly 



* E. Topsent, " Etude Monographique des Spongiaires de France," Archives 

 Zool. Exp. 1895 (3) iii. p. 522. 



Proc. Zool. Soc— 1910, No. IX. 9 



