624 THE FORMS OF TISSUES [ch. 



radiating partitions come to bound narrow and almost parallel-sided 

 interspaces; then it is that the transverse or perichnal partitions 

 begin to come in, and form what the student of the Coelenterata calls 

 the ''dissepiments" of the coral. We need go no further into the 

 configuration and anatomy of the corals ; but it seems to me beyond 

 a doubt that the whole question of the complicated arrangement 

 of septa and dissepiments throughout the group (including the 

 curious, vesicular or bubble-like tissue of the Cyathophyllidae and 

 the general structural plan of the Tetracoralla, such as Streptoplasma 

 and its allies) is well worth investigation from the physical and 

 mathematical point of view, after the fashion which is here shghtly 

 adumbrated. 



The method of dividing a circular, or spherical, system into 

 eight parts, equal as to their areas but unequal in their peripheral 

 boundaries, is probably of wide biological application; that is to 

 say, without necessarily supposing it to be rigorously followed, the 

 typical configuration which it yields seems to recur again and 



Fig. 272. Diagrammatic section of a Ctenophore (^wcAan's). 



again, with more or less approximation to precision, and under 

 widely different circumstances. I am inclined to think, for instance, 

 that the unequal division of the surface of a Ctenophore by its 

 meridian-like cihated bands is a case in point (Fig. 272). Here, if we 

 imagine each quadrant to be twice bisected by a curved anticline, 



