and Physiology of the Spongida. 21 



level with the surface by simply anastomosing with each other 

 through the intervention of the reticular framework of the 

 dermis — or in an intricate reticulated structure with a core of 

 foreign objects, which projects in a conical form beyond the 

 surface — or in the same way, with a core of proper spicules 

 assuming the form of an aculeation. These aculeations, ajrain, 

 may be separate or connected by prominent lines of fibre 

 passing directly between them, which, bearing respectively a 

 fold of the dermal sarcode, thus give a polygonally divided cel- 

 lular aspect to the surface. Or the aculeation may be rounded 

 by the projection of tufts of proper spicules based upon the 

 reticulated fibre of the dermis. Indeed the aculeation always 

 partakes of, and is modified in form by, the nature and com- 

 position of the dermal reticular framework. 



Again, it should be remembered that, although these parts 

 may be frequently bare (that is, uncovered by sarcode) in the 

 fresh as well as in the dry specimen, they were originally in- 

 vested by it, and only became denuded through wear and tear 

 or natural withdrawal of the sarcode. 



Body. 



Having already described the skeleton and the sarcode 

 generally, together with the " sarcode proper " or intercellular 

 substance, as the basis in which all the other structures are 

 imbedded and, as before stated, out of which they are all 

 elaborated, also having described the " dermis," we shall 

 now direct our attention to those parts of the sarcode of the 

 body which have hitherto only been enumerated, beginning 

 with the 



Ampullaceous Sacs. 



When the sponge is fed with carmine or indigo, which of 

 course can only be effected during its active living state, the 

 colouring-matter with the water is drawn into the substance 

 of the sponge through the pores in the dermis, when also the 

 former becomes arrested on the surface of the areolar cavities 

 of the sponge, at points which present a globular or sac-like 

 rounded form. To these points I have heretofore given the 

 name of " ampullaceous sacs," because I found them in Spon- 

 gilla (where I first saw them) of a globular form with a distinct 

 sphinctral opening. They are exceedingly numerous, and may 

 be said, comparing small things with great, to hang about the 

 branches of the excretory canals like grapes in a bunch of 

 this fruit. 



The aperture in this assumed sac (for the sarcode, which is 

 probably of the " intercellular " kind, is too subtle to present 



