On tJie Structure of the Stjlasterida;. 191 



to the Hydroidea*, dwells on the utter impossibility of Acalephs 

 formiug corals with distinct septa ; yet in Criiptohelia and the 

 fStylasters septa are present in the corallum, which in many cases 

 so closely resemble those of Zoantharian corals that these corals 

 were placed by Milne-Ed\\'ards in the Oculinidae, and the septa 

 were never suspected to be pseudo-septa until 8ars t observed that 

 in Allopora oculina the tentacles (tentacular zooids) were situate 

 between the septa, and not upon them. I should not have de- 

 tected the compound nature of the calicular gi'oups in Stylaster 

 had I not been led up to the fact by the examination of other 

 genera of the family, in which the tentacular zooids are widely 

 separated from the alimentai'y ones. The determination of the 

 compound nature of the calicular groups at once explains the 

 otherwise very anomalous arrangement of the pseudo-septa in many 

 Stylasteridse. The condition existing has been described J as a 

 " tendency of the septa to unite by their inner edges and enclose in 

 the interseptal chamber thus formed the septa of a higher order." 

 The real explanation of the matter is that the apparent interseptal 

 chambers are the pores or calicles of the tentacular zooids. In 

 those species in which the tentacles are removed from harm's way 

 in the retracted condition of the coral by being bent inwards down 

 into the wide cavity containing the alimentary zooid (calicular 

 cavity), these pores have their walls incomplete on the side nearest 

 to the calicle, and take the form at their mouths of elongate slits, 

 in order to allow of this inward inclination of the contained tentacu- 

 lar zooid when at rest, or when feeding the deeply seated alimen- 

 tary zooid. The supposed included septa of higher order are the 

 styles of the tentacular zooids. In some forms of the family these 

 styles are brush-like in shape, just like the central styles of the 

 alimentary zooids ; they have this form in Allopora miniacea §, 

 and less markedly in Stylaster complanatw^, Pourt. || In some 

 Stylasteridse, as e. g. in Stylaster amphiJielioides, 8. Kent ^, there 

 is no appearance at all of pseudo -septa. The pores of the tentacular 

 zooids are simple circular-mouthed pits, arranged in a circle around 

 the large pore of the alimentary zooid. In Allopora subviolacea, 

 S. Kent** , the pores of the tentacular zooids are, in some zooid 

 groups in the same specimen, mere pores ; in others slits com- 

 municating with the cavity of the pore of the alimentary zooid. 

 The irregularly scattered condition of the zooids existing in Poly- 

 pora is to be regarded as the primitive one in genesis from which 

 that existing in Stylaster amphiJielioides and that in Allopora sub- 

 violacea represent transitional stages towards the high specializa- 

 tion of the zooid groups found in Cryptohelia and other species 

 at present termed Stylaster. 



* Prof. A. E. Verrill, 'Ann. & Mag. Nat. Hist.' 1872, 4th ser. vol. ix. p. 358. 

 t Forh. Selsk. Christ. 1872, p. 115. } Pourtales, /. c. p. 33.^ 



U Pourtales, I. c. pi. iii. fig. 15. || Pourtales, I. c. pi. ii. fig. 17. 



% Saville Kent, I. c. pl.xxiv. fig. \c. ** Ibid. pi. xxv. fig. 2 a. 



