AFFINITIES AND ZOOIOGICAI POSITION. 71 



recognise their existence in some part or another of tangential 

 sections, and have no doubt that they are in this species 

 really present throughout the whole of the peripheral part of 

 the skeleton. Their special interest arises from their being 

 in appearance precisely similar to the "septal spines" of so 

 many species of Favosites (using the term " septal " in its 

 proper signification). 



(b) Transverse Sections. — The appearances presented by 

 transverse sections vary according to the part of the section 

 which may be looked at. The central portion of such a 

 section exhibits the tubes in the axial portion of the branch 

 divided at rio^ht angrles. In the circumference of the section, 

 on the other hand, the tubes are divided more or less nearly 

 longitudinally, owing to their curvature on nearing the surface ; 

 while this part also shows them in the thickened condition 

 which they possess in the cortical portion of the branch. 

 The appearances presented by the periphery of transverse 

 sections are therefore the same as those shown in the corre- 

 sponding region in longitudinal sections, and need not be con- 

 sidered till we come to speak of the latter. In the central 

 region of a transverse section (fig. 9, b) we can study the con- 

 dition of the tubes in the axis of the branches before they bend 

 outwards to the surface ; and we find that their structure is 

 very different from that which they possess in the cortical 

 region (as seen in tangential sections). Instead of being 

 rounded and thick-walled, and provided with a largely de- 

 veloped canal-system, they are now thin-walled, and angular 

 or polygonal in shape, and the canaliculi of the wall seem to 

 have totally (or almost totally) disappeared. There is also an 

 apparent total absence of the radiating spines which are de- 

 veloped in the cortical part of the tubes. Lastly, the tubes in 

 this region appear to be almost entirely, or entirely, referable 

 to the proper zooecia, the interstitial tubes or cancelli existing 

 only, or mainly, in the cortical region. 



(c) Longitudinal Sections. — These show precisely the same 

 differences, as regards their central and peripheral portions, as 



