46 



THE GENUS MONTICULIPORA. 



to that reached by the smaller tubes of the colony. Tangen- 

 tial sections taken a little below the surface (figs. 4 and 5) 

 show that these apparent spines are composed of concentrically 

 laminated sclerenchyma, exhibiting in their centre a dark 

 circular spot or a clear circular space. There cannot, there- 



Fig. 4. — Portion of a tangential section of 

 Monticulipora implkata, Uliich, showing 

 the hollow intracalicine spines, enlarged 

 fifty times. From the Cincinnati Group 

 of Ohio. 



Fig. 5. — Portion of a tangential section of 

 Alonticiilipora nionilifo7-mis, Nich., show- 

 ing the intracalicine spines, enlarged 

 fifty times. From the Hamilton Group 

 of Ontario. 



fore, be any doubt but that these structures are primitively 

 hollow, though their central cavities often appear to become 

 filled up by a secondary deposit of sclerenchyma, as growth 

 proceeds. In this primordial hollowness of the spines is to be 

 found, I believe, the real clue to their nature ; and I can hardly 

 doubt that instead of being merely appendages of the corallum, 

 they are truly of the nature of peculiarly modified zooids or cor- 

 allites.^ The correctness of this view is most readily recognised 

 when we come to examine thin sections of those forms which 



^ These peculiar hollow spines have been described and accurately figured in 

 various Monticuliporoids by Dybowski (Die Chsetetiden, p. 9, &c.), under the 

 name of " Wandrohrchen " or " Porenkanalchen." He regards them as of the same 

 nature as the peculiar canals (" intramural canals") which are found in various 

 "Tabulate corals" (such as Colnmnopora, Lyopora, Pleiirodictywn, &c.) The 

 "intramural canals" of forms such as those above mentioned are, however, not 

 bounded by distinct proper walls of their own, and are quite irregular in their dis- 

 tribution. For these reasons, amongst others, I cannot regard them as being in any 

 way comparable with the " spiniform corallites" of the Monticuliporoids, and I 

 must in the meanwhile adhere to the views expressed in the text as to the nature 

 of these latter structures. 



