492 A MONOGRAPH OF THE AUSTRALIAN SPONGES, 



So long however as no direct proof for this has been brought 

 forward, it will be well to suppose that the inhalent canals have 

 been produced before the sub-dermal cavities and the very constant 

 pore-sieves on the surface ; and that no secundry process of ramifi- 

 cation, occurring after the sponges possessed pore-sieves, sub-dermal 

 cavities, &c., has ever lead to the formation of true inhalent canals 

 below the skin. 



Numerous difficulties present themselves in connection with the 

 formation of the inhalent canals by implication, and here in the 

 sponges with complicated sub-dermal cavities particulaily Marshall's 

 hypothesis of an entodermal oi-igin of these canals may come near 

 the truth. 



While this result of the study of the comparative anatomy of 

 the canal system corroborates the theory established by F. E. 

 Schulze (1) that the sponges are ontogenetically formed by a con- 

 tinued process of folding, to which I referred in my last paper on the 

 Auleninse (2) ; it shows at the same time that some of the oscular 

 tubes, and very likely all which are very highly developed and 

 large, are formed by an invagination of the outer skin and are 

 accordingly clad with ectodermal cells. The limit between 

 ectoderm and entoderm need therefore not necessarily be situated 

 on the margin of the osculum. 



Whilst in some Auleninse, particularly Halme, the sand-armour 

 is developed in the outer skin only, we find here, and also in 

 Euspongia canaliculata no difierence in the structure of the skin 

 on the outer surface and in the vestibule spaces of the interior : 

 the formation of these spaces in Eusjjongia and Hippospongia is a 

 more recent acquirement. 



The development of the vestibule is different in the different 

 varieties of Euspongia irregularis. In Euspongia irregularis 

 silicata the vestibules form anastomosing and very much curved 



(1) F. E. Schulze. Uiitersuchuugen liber den Bau und die Entwickelung 

 der Spongien IX., Mittheilung, Die Plakmiden. Zeitschrift fiir wissen- 

 schaftliche Zoologie. Band XXXIV., Seite 438. 



(2) R. von Lendeitfeld. A Monopraph of the Australian Sponges, Part V., 

 The Auleninai. Proceedings of the Linnean .Society of New South Wales. 

 Vol. X., part 3. 



