72 THE GENUS MONTICULIPORA. 



have been already noted in transverse sections ; but it is now 

 necessary to briefly direct attention to both parts of the sec- 

 tion (fig. 9, c and d). In the central portion of the section 

 (supposing the slice to be taken in the median plane) the 

 tubes are seen in the axial portion of their course, where they 

 are nearly vertical, and where they exhibit the features which 

 I have pointed out as characterising them in the central region 

 of transverse sections. That is to say, they are here provided 

 with thin and delicate walls, in which the canal-system of the 

 cortical region seems to be very slightly developed or want- 

 ing. The chief point to notice about the tubes in this part of 

 their course (and it is one that I have never failed to recog- 

 nise) is, that their cavities are here crossed by transverse cal- 

 careous plates or " tabulae " (the " septa " of Professor Busk and 

 Mr Waters), which, though few in number, are "complete" 

 and in every way well developed (fig. 9, c). 



On the other hand, in the peripheral portion of their course 

 (where the appearances are precisely the same as in the 

 corresponding region of a transverse section) the tubes have 

 very much thickened walls, and the walls are crossed at right 

 angles by numerous canallcull, which open at both ends into 

 the cavities of the tubes by trumpet-shaped apertures. In 

 all parts of the section, also, where the inner surfaces of the 

 tubes are brought Into view, these exhibit numerous rounded 

 apertures or pores, which represent the mouths of the said 

 canaliculi, and which have been well described and figured by 

 Professor Busk and Mr Waters {loc. cit.) It is very difficult 

 in the outer part of these longitudinal sections to distinguish 

 between the proper zooecia and the interstitial tubes or can- 

 celli, their size being very much the same, and their internal 

 structure being exactly alike ; and this leads me to make a 

 few remarks upon another point. When, namely, such a 

 section as I now speak of Is examined with the ^-inch ob- 

 jective, it is seen that the wall separating contiguous tubes 

 exhibits a central light space, limited on both sides by dark 

 and definite boundaries, and crossed by the transverse canall- 



