THE STEUCTUEE AND EELATIONS OP TUBIPOEA. 573 



tabulae of Syringopora, for they are found to be exceedingly 

 friable and perforated by numerous small holes, just as they 

 are in Tubipora. 



The corallum of Syringopora springs from a prostrate net- 

 work of tubes ; in Tubipora it springs from a prostrate stolon, 

 which, as I have shown, contains a network of canals. The 

 prostrate network of tubes in Syringopora was in contact with 

 rocks and stones at certain places; the stolon of Tubipora is in 

 contact with its support only in certain places, and at others 

 rests upon no support, so that I think we have sufficient 

 evidence to assume that these two structures are really 

 homologous. 



The presence of tabulae in Syringopora, which was formerly 

 considered to be a strong point in favour of the Zoantharian 

 affinities of the genus, has become, since our knowledge of the 

 structure of Tubipora has increased, an argument in favour of 

 its Alcyonarian affinities. In addition to the striking similarity 

 in shape between the tabulae of Syringopora and Tubipora, 

 the general shrunken appearance they have in the former genus, 

 as shown in the numerous figures given by Professor Nicholson 

 (19, 20), goes to prove that they are due in this genus too to a 

 shrinking of the mesoderm, and that consequently they are in 

 every respect homologous. 



A very great difficulty, however, that is found by Professor 

 Nicholson and others in regard to the Alcyonarian affinities of 

 Syringopora, is the undoubted relationship which exists between 

 this genus and the family Favositidae, which family is considered 

 by them to be undoubtedly Zoantharian, and closely allied to 

 Porites. But the evidence in favour of the Favositidae being 

 really Zoantharians is by no means conclusive, for it seems to rest 

 entirely upon the presence, in some cases only, of spiniform 

 septa iyi the corallites.^ The presence of tabulae is no longer 

 evidence against their being Alcyonaria, as Professor Moseley 

 has shown that Heliopora, which possesses tabulae, is un- 

 doubtedly an Alcyonarian and Tubipora, also is now known 

 to possess true tabulae. In fact, when we remember that tabulae 

 * In Stenopora septal spines are absent. 



