STUUCTUKE OF SERIATOPORA, POCILLOPORA, ETC. 395 



The longer axis of the mouth is always in these corals directed 

 parallel to the direction of extension of the branches, and the 

 polyps are so disposed that the mesenteries bearing filaments are 

 placed always in the direction of the bases of the branches. Similar 

 indications of a regular orientation of the polyps are to be seen in 

 the coralla of the genus Madrepora and other genera. Although 

 in Cerianthus and Edwardsia a dorsal and ventral differentiation 

 of structure is well marked, there is no indication of such in 

 the Actiniadse, excepting in their early stages of development, and 

 in very many simple and compound Madreporaria there seems 

 to be no indication of such in the coralla. 



In the Turbinolidge, for example, there is no trace of such 

 differentiation, and there is also none in the Oculinidse. It seems 

 probable, therefore, that the af&nities of Seriatiopora, and Pocillo- 

 pora which is certainly nearly allied to it, do not lie with this 

 latter family ; but it is almost useless to speculate as to what 

 their real position amongst the Madreporaria may be until the 

 structure of the soft parts of more representatives of this group 

 are known. lu not having their mesenteries disposed in pairs, 

 with regard to the septa, they differ from other Madreporaria 

 as yet investigated. 



It is worthy of remark that the pair of mesenterial filaments 

 present in Seriatopora and Pocillopora cannot, according to the 

 system of development of the six pairs of mesenteries of Adamsia 

 diapJiana discovered by the brothers Hertwig,^ correspond with 

 the first pair of filaments developed in the larva according to 

 Lacaze Duthiers, viz. those belonging to the primary pair of 

 mesenteries of the larva. 



In Adamsia, according to the Hertwigs, the lateral pair of 

 mesenteries are the fifth and sixth pairs in order of appearance, 

 and probably, though they make no statement on this point, 

 the mesenterial filaments belonging to them follow the same 

 order in development. According to Lacaze Duthiers^ account 

 of the order of appearance of the mesenteries in Actiniadse the 

 mesenteries bearing the filaments in Seriatopora would corres- 

 pond with his primary ones if the orientation of most of his 

 figures were transposed, and the position taken up by the 

 primary mesenteries regarded as ventral instead of dorsal when 

 compared with Seriatopora.^ There are at present no reasons 

 for orienting these solitary forms in one way rather than the 

 other, and it will only be possible to obtain such reasons by 

 tracing completely the development of some compound Madre- 

 porarian, such as Pocillopora. 



1 0. and H. Hertwig, " Die Actiuien," ' Jenaische Zeitsclirift,' 13 Bd., 

 4 Heft, 1879, S. 545, Taf. xvii, fig. 3. 



* See Lacaze Duthiers, ' Arcli. de Zool. Exp. et Gen.,' vol. i, 1877, 

 p. 59, fig. 6. 



