PROTOZOA AND SPONGES 



quite at random without rule or arrangement. And yet 

 there is an arrangement discernible here; for the canals 

 are formed by the manner in which these are grouped; 

 and this is seen much more clearly, in the case of the 

 three-rayed needles of lime in the Grantice. Mr. Bower- 

 bank has shown that in 6 t . compressa the substance is 

 divided into very regular chambers in a double series, 

 separated by a diaphragm, whose axis is at right angles 

 to the axis of the sponge; and that these chambers are 

 denned by walls made up of the three-rayed needles in 

 their mutual interlacement. 



