

BY R. VON LEXDEXFELD, PH.D. 313 



The color may be diffuse, but is also often exclusively found 

 in granules which may be imbedded in the gallert or in the cells 

 of the Sponge. 



Of the changes which the colours of Sponges undergo when 

 dying, those are most remarkable, which are met with in the 

 yellow Aplysinidaa and Apjysillidse, they turn dark blue. 



3. Internal structure. 



The skin or outermost layer of the Sponge is often only loosely 

 connected with the main part of the body, and can be removed 

 from the concave fields between the conuli. 



The body appears on a transverse section, more or less porous. 

 The pores are the orifices of the channels which traverse the 

 body of the Sponge in every direction. The lumen of these 

 canals varies very much so that in some cases the Sponge appears 

 very porous, only about 30% of the space being taken up by the 

 Sponge substance itself, whilst all the rest is canals. In other 

 cases again the canals become rare and narrow and are often 

 quite invisible. This, for instance, often occurs, when a living 

 Sponge is cut, because the whole of the body contracts so much 

 that all the vacant space is filled up by the Sponge tissue and all 

 the water ejected. 



Also the hardness is subject to great variations. Some Sponges, 

 without skeleton, appear very soft, nearly slimy ; whilst others 

 again, particularly the Lithistida?, attain the hardness of a stone. 

 But not only does the skeleton make a difference in this respect, 

 the ground substance of the Sponge itself varies greatly in its 

 density between the slimy appearance of a soft gallert and the 

 resistent form of cartilage. 



4. The Canal-system. 



The canals are mostly crooked and irregular, only in a few 

 Sponges they appear, as more or less, parallel and straight tubes. 

 Their breadth varies very much, although it often happens that 

 they will all appear of the same width in a section. From the 



