68 THE GENUS MONTICULIPORA. 



hardly recognisable. The cancelli, In fact, are often nearly 

 or quite as large as the proper zooecia (see fig. 8, b and c) ; 

 and the chief distinction between them rests upon the gen- 

 erally more clearly angular shape of the former, and upon 

 their mouths not being at all raised above the general surface. 

 As regards the intei'iial striictui''e of Heteropora neozeianica, 

 the skeleton, as of the species of Heteropora generally, Is 

 ramose or dendroid ; and the branches resemble those of any 

 similarly shaped coral in being composed of fasciculate tubes 

 which are nearly vertical in the axis of the branch, but ulti- 

 mately bend outwards to reach the surface. We can thus 

 divide each branch Into an axial and a peripheral or cortical 

 portion ; and not only do the tubes in these two portions 

 of their course differ in directiojt, but they are markedly 

 different (as we shall see) In their actual striicture. That 

 is to say, the structure of any particular tube is exceedingly 

 different, according as we examine it In the axial or in the 

 cortical part of its course. Moreover, it is in the cortical 

 portion of the skeleton alone, or almost alone, that the in- 

 terstitial tubes are developed, the axis consisting wholly, or 

 almost wholly, of the proper zocecia. We cannot, therefore, 

 arrive at a proper understanding of the true structure of 

 Heteropora (or of any similarly constructed skeleton) without 

 making three distinct sections, — viz., one parallel to the surface 

 and just below it, which we may call tangential, and which is 

 the most Important of all, as giving us the cross section of 

 the tubes in their final and most fully developed condition ; 

 secondly, one at right angles to the branch (a transverse sec- 

 tion) ; and thirdly, a loJigitudinal section, dividing the branch 

 vertically through its median plane. The following are the 

 principal points brought to light by an examination of these 

 three sets of sections in H. jieozelanica : — 



(a) Tangential Sections. — As just remarked, there are no 

 sections which yield more interesting and valuable results 

 than those which intersect the skeleton tangentially, just below 

 the surface upon which the tubes open. When we examine 



