396 H. N. MOSELEY. 



It is not at all improbable that the presence of a single pair of 

 mesenterial filaments only in the forms under consideration may 

 have no more ancestral significance than the survival of the 

 dorsal pair only in the siphonozooids of Alcyonarians, and in the 

 young Pocillopora possibly traces of all twelve filaments might 

 exist. An ancestral twelve has probably been reduced by natural 

 selection to the present two, but it would be of interest if it could 

 be shown that the pair thus surviving is that which is earliest 

 developed in the larva. 



I hope soon to publish a fuller account of the structure of 

 Seriatopora, accompanied by figures. I have as yet had no time 

 to prepare any sections. 



To sum up, Seriatopora is undoubtedly Madreporarian. 



The important points in its structure are the presence in it of 

 a highly-developed vascular system similar to that existing in 

 Alcyonarians ; the fact that each polyp has only a single pair of 

 mesenterial filaments, and that these filaments are lodged in 

 pouches resting in special deep pits in the corallum, that only 

 the mesenteries bearing the filaments develop sexual organs, that 

 the coral stocks are unisexual, that in the structure of the polyps 

 a differentiation into a superior or dorsal and inferior or ventral 

 region is clearly indicated both in the soft tissues and in the 

 corallum, and that the polyps in each stock are arranged with 

 regularity with the dorsal ends of their oval calicles turned 

 towards the tips of the branches, and their longer axes parallel 

 to the lengths of the branches, in this respect agreeing with 

 Alcyonarians. 



Corallium rubrum. 



When examining the soft structures of Corallium rubrum by 

 means of decalcification, in the beginning of the present year, 1 

 paid special attention to the small polyps which appear as 

 minute white points scattered on the coeuenchym around and 

 amongst the main large sexual polyps. I found that they are 

 small polyps devoid of tentacles, just as described and figured by 

 Prof. Lacaze Duthiers in his classical memoir, but I further 

 noticed facts which he does not mention, namely, that these 

 polyps have their dorsal and ventral pairs of mesenteries deeper 

 than the lateral pairs, and possess only a single pair of mesen- 

 terial filaments, the dorsal. Hence they agree in every particular 

 in structure with the siphonozooids ^ of Sarcophyton and other 

 Alcyonarians, in which two kinds of polyps, autozooids and 

 siphonozooids, occur. Prof. Lacaze Duthiers paid especial atten- 



' "Report on the Scientific Results of the Voyage of H.M.S. Challen- 

 ger," ' Zoology,' vol. ii, 1881, p. US. 



