THE MONTICULIPOROIDS. 353 



2. The Monticuliporoids increase by fission as well as by gemmation, 

 whereas the recent Polyzoa appear to be uniformly characterised by a 

 gemmiparous mode of development, which varies in its precise details in 

 different groups. Moreover, the gemmation of the Monticuliporoids is 

 " intermural," and is precisely similar to that which obtains among the 

 Favositidce. 



3. " Ccenenchymal gemmation " occurs in the Fistuliporidce, this mode 

 of increase being otherwise absolutely characteristic of Heliopora and of 

 the Heliolitidce. 



4. The walls of the tubes in the Monticuliporoids are imperforate ; 

 whereas in the calcareous Polyzoa the skeleton seems to be almost 

 always (probably always) porous, and the cavities of contiguous cells are 

 usually placed in direct communication by means of connecting-foramina 

 or tubes. 



5. The abundant development of " tabulae " in the Monticuliporoids is 

 a feature in which these organisms resemble a large number of un- 

 doubted Corals. 



6. Certain Monticuliporoids possess in their autopores radial folds or 

 plications which may be compared with the " pseudosepta " of Helio- 

 pora; while others (Monticulipora mammulata) possess radially disposed 

 calcareous spines, which are closely similar to the septal spines of Favos- 

 z'tes, of Syringopora, and of certain species of Heliolites. 



On the other hand, there are the following considerations which 

 would point to a relationship between the Monticuliporoids and the 

 Polyzoa, or which, at any rate, would more or less diminish the import- 

 ance of some of the features above mentioned as showing the Ccel- 

 enterate affinities of these organisms. 



1. The polyzoary of Heteropora (which is undoubtedly a Polyzoan) 

 consists of large tubes scattered among smaller ones, though there does 

 not appear to be any essential difference in the structure of these 

 respectively. 



2. " Tabulae " are by no means confined to the Ccelenterates, precisely 

 similar structures — so far as appearance goes — being present in un- 

 doubted Polyzoa {e.g., in Heteropora, Domopora, Fascicularia, Alveo- 

 laria, &c.) 



3. Radial structures in the form of rows of spines are present in a 

 number of Polyzoa {e.g., in Heteropora, Discoporella, &c.) 



4. There are various Polyzoa (such as Rhombopora Hamiltonensis, 

 Ceriopora mterporosa, and some of the Fenestellids) which possess struc- 

 tures apparently very similar to the " acanthopores " of many Monti- 

 culiporoids. Structures presenting in some respects the same aspect are 

 found in the recent Reteporo?, in which they serve to carry the avicularia. 



5. Portions of the skeleton of Fistulipora incrustans, PhilL, have been 

 shown by John Young to become thickened, and to exhibit a finely 

 tubulated structure similar to that seen in the skeleton of the Fenes- 

 tellidce. 



6. According to the observations of Lindstrom, certain of the Monti- 

 culiporoids pass through early stages of development in which the 

 skeleton is of a distinctly Polyzoan type. As an example of this, we 

 may take the singular Callopora heterosolen, the basal (and therefore 

 first-formed) portion of which exhibits Polyzoan characters, while the 

 main mass of the skeleton is of the ordinary Monticuliporoid type. 



VOL. 1. z 



