BY R. VON LENDENFELD, PH.D. 491 



This tabular view of the developement of the canal system of 

 course does not indicate that the species mentioned as examples 

 are descended from one another. But it shows how the common 

 gastread ancestor developes into the most highly difFerentiai,ed 

 sponges by a continued process of folding. 



The table is the result of the study of the comparative anatomy 

 of the canal system. Transition forms are met with throughout. 

 Of particular interest are those described by me (I) of Cacospongia 

 exemplum which lead from stage 5 to 8a in a peculiar manner and 

 the peculiar structure of Aphrodite Nardorus, described by me in 

 the same paper (2). Some statements regarding the developement 

 of the canal system of Calcareous sponges will be found in Part 

 III., of this Monograph (3). 



Of particular interest also is Dendrilla rosea (4) in as much as 

 the oscula tube of this species possesses under its wall, small 

 sub-dermal cavities, similar to those under the outer skin, only 

 smaller. 



At the time I drew attention to this extraordinary structure, I 

 do not doubt now, that these sub-dermal cavities are a rudimentary 

 oi-gan indicating that this oscular tube is being formed from an 

 inverted portion of the outer skin. It represents one of the last 

 transision forms between the stages 7a and 8a. 



No further developement of the stage 7b has as yet been observed, 

 but it may be assumed that some sponges with a very highly 

 developed inhalent canal system, and particularly those which 

 possess sensitive cells in the diaphrgms which pervade the inhalent 

 canals, have obtained their inhalent canal system by a secundry 

 plication of the ectodermal wall. 



(1) E. r. Leiuh'vfeld. A Monograph of the Australian Sponges, Part V. 

 The Auleninse. Proceedings of the Linnean Society of New South Wales, 

 Vol. X., parts. 



(2) R. V. Lendenfeld. L.c. 



(3) R. V. Lendenfeld. A Monograph of the Australian Sponges, Part III. 

 The Calcispongiffi . Proceedings of the Linnean Society of New ^outh Wales, 

 Vol. IX., p. 108.3 flf. 



(4) R. V. Lendenfeld. Ueber Coelenteraten der Stidsee, II. Mittheilung, 

 Neue Aplysinidse. Zeitschrift fur wissenschaftliche Zoologie, Band 

 XXXVIII., Seite 277. 



