BY R. VON LENDENFELD, PH.D. 559 



by closing the pores, and in every way the whole cavity 

 appears as an excellent nursery. It is, however, not often 

 that one finds this cavity tilled with embryos, generally there are 

 no larvae at all in it, and it seems that they are kept there for a 

 short time only, 



I am not inclined to believe that these cavities were originally 

 produced to serve as a nursery, but we could easily understand 

 how, after pseudoscula once had been formed by a process 

 of secundary folding as in Halme and other sponges ; (1) 

 these had been turned into a nursery, and how a poresieve, 

 similar to the structures covering the entrances of the inhalent 

 system had been formed over it, so as to adopt it better to its new 

 function. 



But even if we attach less value to the breeding functions of 

 this cavity, we still find that the formation of such a membrane 

 was of great importance to the sponge, because it could by its 

 means regulate the water current to a great extent. 



Vestibule cavities belonging to the inhalent system and similar 

 to those of our sponge have been described by me from Euspongia 

 canaliculata (1. c.) These have no covering membrane, In 

 several siliceous sponges belonging to the genus Syphonocholina I 

 have found similar perforated membranes which are homologous to 

 the membranes described above. 



Histological Structure. 



I have examined the vestibule membrane, as I shall in future 

 designate the structure here described, very minutely, and the 

 results of a study of section series and surface views, are the 

 following : — 



Seen from the surface under a low power the membrane appears 

 perforated by numerous circular holes which are distributed very 

 regularly. (Fig. 2.) Their diameter is, as mentioned above, of 

 course subject to very great variations. Their centres are on an 



(1) R. von Lendenfeld. A Monograph of the Australian sponges, Part 

 VI. Proceedings of the Linnean Society of N.S.W., Vol. X. 



