ON THE POSTEMBRYONIC DEVELOPMENT OF CYCLOSERIS. 175 



septa of the first four cycles can be distinguished (Fig. 14). The aboral surface round 

 the scar has been much overgrown b\^ Polyzoa, and in the smaller free form the corallum 

 is very dense round it so that the costae cannot be traced into its septa. Another 

 specimen triangular in shape, 25 mm. in diameter, has the scar very distinct with 

 the costae quite continuous into its septa (Fig. 17): it has also been overgrown by 

 organisms except for a few mm. round the edge. A larger anthocyathus 53 mm. in 

 diameter has the scar still distinct with the septa quite visible (Fig. 16); otherwise 

 its characters are those of the adult. The oral and aboral surfaces of the latter are 

 represented in Figs. 15 a and 15 b. The scar has been completely obliterated and 

 covered over by corallum, its position being merely indicated by a slight opacity. 



The striking resemblances between the developments of Cycloseris and Fungia 

 cause a doubt as to the distinctness of these two genera. The differences, mentioned 

 above, between them, are undoubtedly worthy of generic rank, but the two forms are 

 evidently extremely closely allied. The primary septa in Cycloseris are very definitely 

 six in number, the secondaries not reaching quite so faf into the calice and having 

 the tertiaries fused to them. In the youngest instar that I examined there are six 

 thick, subequal septa, and in the youngest Fungia found by Bourne " twelve septa 

 are present of which six are distinctly larger than the others." In nearly all the 

 solitary imperforate Madreporaria, which are the more ancient in respect to time, six 

 septa are very strongly marked, and must be regarded as the primaries. In many 

 forms too only six septa are present, and these so far as is known are always 

 entocoelic. The formation of twelve septa simultaneously in Astroides calycularis, of 

 which six later get larger, I can only regard as a condensation of the stages of its 

 development 1 . It seems to me that primitively there are six entocoelic septa, a 

 number that corresponds with the twelve mesenteries found in the embryos of many 

 of the Actiniaria, and in the embryo also of Euphyllia 2 at the same stage apparently 

 as the fixing larva of Astroides calycularis. 



In conclusion, I wish to thank Mr Adam Sedgwick, Dr Willey and others for 

 their kindly interest and advice. 



Zoological Laboratory, 

 ( Iambrtdge. 



Augutt 21, 1898. 



1 Vide " Developpement des Coralliaires." H. de Lacaze Duthiers. Arch, de Zool. Exper. et Gen., I. and 

 II. (1872 and 1873). Also G. von Koch, Mitt, aus der Stat. Zool. Xeapel, in. 1882, p. 284. 



2 " The Newly-Hatched Larva of Euphyllia." A. C. Haddon. Sci. Proc. Roy. Dublin Soc, p. 117, 1890. 



