352 THE MONTICULIPOROIDS. 



precisely similar to that which obtains in the Favositidce. It is for 

 this reason that rough fractures of the Monticuliporoids expose the 

 walls of tubes, whereas in the genus Chmtetes, where the growth is 

 fissiparous, fractures usually lay open the visceral chambers of the 

 corallites. It is, however, interesting to note that fission also occurs 

 not rarely in the Monticuliporoids, though it is not so common a 

 mode of increase as gemmation. In the mesopores of Fistulipora 

 and some allied types fission seems to be the ordinary mode of 

 increase, as it is in the case of the siphonopores of the Heliolitidce. 

 This fact would go far to prove that the mesopores are not merely 

 ccenenchymal ; since fission can hardly occur unless we suppose the 

 existence of separate zooids endowed with the power of division. 

 The occurrence of fission in the autopores of the Monticuliporoids 

 is also strongly against the reference of these organisms to the 

 Cyclostomatous Folyzoa, since these latter invariably increase by 

 means of gemmation. A still more interesting fact is the occur- 

 rence — as described by Waagen — of "ccenenchymal gemmation" 

 among the Fistuliporoids, autopores in these cases being formed by 

 the abortion and apparent fusion of a group of mesopores, in a 

 manner precisely similar to that previously noted as occurring in 

 Heliopora and Heliolites. This fact would also bear very strongly 

 against the view that the Monticuliporoids are to be regarded as 

 belonging to the Folyzoa. 



It must be admitted, however, that the zoological affinities of the 

 Monticuliporoids are still a matter of uncertainty. In many of their 

 features, both structural and developmental, they show marked rela- 

 tionships with the Actinozoa generally, and with the Alcyonaria in 

 particular, while in others they approach the Folyzoa; and it must, 

 in the meanwhile, remain a matter of individual opinion whether the 

 Monticuliporoids should be regarded as a very peculiar group of 

 Corals or as an equally peculiar group of Polyzoans. It would be 

 out of place here to enter into any detailed discussion of a question 

 so complex, but it may be of advantage to summarise briefly the 

 chief points which must be taken into consideration in coming to 

 any decision as to the systematic position of the Monticuliporoids. 



Leaving the external form of the skeleton entirely out of con- 

 sideration, the general features which favour the reference of the 

 Monticuliporoids to the Cazlenterata are the following : — 



i. The common dimorphism of the colony in the Monticuliporoids 

 finds its best parallel in Heliopora and Heliolites, the Ccelenterate nature 

 of which is undoubted. In particular, the structural relationships between 

 Fistulipora and Heliolites, or Plasmopora, are exceedingly close ; the 

 skeleton consisting in both of large, sparsely tabulate tubes ("autopores ") 

 separated by smaller, closely tabulate tubes (" mesopores " or " siphono- 

 pores "), and the former of these possessing radial structures of the nature 

 of " septa " or " pseudosepta." 



