BY R. VON LENDENFELD, PH.D. 291 



These large lacunae in the interior are also in communication 

 with one another by so large apertures in the dividing lamellje 

 that they must be considered as continuous. (Plate XXVII., 

 figs. 4, 5.) The lamellse between these pores are the true body of 

 the sponge, they are irregularly bent and twisted, and on an 

 average 1 mm. thick. This system of lacunae connected with the 

 outer seawater by numerous large pores is a structure different to 

 anything hitherto known in sponges. All these lacunae together 

 can be very correctly designated as a vestibule or anti-chaudjer, 

 and the name of the subfamily is derived from this peculiarity. 

 Into these lacunsee the oscula open, and from them also the 

 inhalent canals originate. 



If we were to imagine an ordinary sponge to grow in very thin 

 lamellae, that these lamellae coalesce in parts and form a honey- 

 comb structure as in the beautiful and large Echispid mentioned 

 above and that further from the free margins of the lamellae a 

 dermal membrane were to grow out, which surrounded each 

 opening with a fringe of varying development ; we would have a 

 sponge before us which in this respect would be like Halme. 



That, as here stated, these lacunae do not belong either to the 

 inhalent or exhalent system is conclusively proved by the fact, 

 that in the surface of the lamellae between them, both inhalent and 

 exhalent pores are found. 



The Significance of the Vestibule to the Sponge. 

 It is perhaps difficult to see what advantage the sponge may 

 derive from this peculiar structure. "We might assume that the 

 raison detre of it is the following : — • 



1. It is disadvantageous to the sponge to load its outer surface 

 with a hard pavement of cemented sand granules, which pavement 

 of course greatly impedes the movements of the pores, and conse- 

 quently also the regulation of the water current. 



2. It is advantageous to any sponge to be defended by a hard 

 armour of cemented sand on its surface. 



The effect of the combined action of these two regulatives during 

 the ordinary course of evolution, might be the peculiar structure 

 just described. 



