Haddon and Shackleton — A Revision of the British Actinice. 623 



two elements of each pair are respectively a perfect and imperfect mesentery, and 

 are independently developed. Recently, however, Danielssen (1890) has thrown 

 doubt upon this paired arrangement, since he finds in the various species he has 

 examined that the muscles are equally developed on both sides of the perfect 

 mesenteries. Owing to the kindness of our Norwegian colleague we have been 

 enabled to examine some specimens of Ejnsoanthus [" Mardcelf^l^ erdfnanni, and our 

 sections show this paired arrangement quite clearly. 



Gonads. — There appears to be a general impression that all the Zoanthese are 

 hermaphrodite. This is certainly not the case in four genera ; of one genus we 

 have no facts either way, and in the the remaining two genera the sexes may be 

 distinct or united. Generative organs often appear to be absent in specimens of 

 Zoanthese, but we have been somewhat fortunate in finding them in those 

 we have examined. Their mode of occurrence will be seen on reference to the 

 Plates in this and in the Memoir on the Zoanthese from Torres Straits. 



Erdmann found that the two species of Zoanthus which he examined ("1 sp. 

 Zoanthus sp. ?," p. 438 ( = Z. dance [?], Hertwig) ; and "2 sp. Z. sp. ?," p. 447) 

 were hermaphrodite, so he concluded that this was a generic character. M^Murrich 

 found no generative organs in the two species he examined. Of the three 

 species we have examned, two specimens of Z. coppingeri were male and three 

 were female ; two specimens of Z. jukesii were female, and of the four specimens of 

 Z. macgillivrayi we sectionized none were fertile. The conclusion we arrive at is 

 that the genus is as often dioecious as monoecious. 



M°Murrich found that Isaurus \J' Mamtnillifera"'] tuherculatiis was hermaphro- 

 dite, and owing to his courtesy we have been enabled to verify this fact. We 

 have cut several specimens of our /. asymmetriciis, but in only one of them could 

 we discover generative organs, and in this case they were feebly developed ova. 

 We cannot, however, assume that the genus is hermaphrodite because one 

 species is undoubtedly monoecious. 



All the remaining genera, so far as is known, are dioecious, except Sphenopus, 

 the gonads of which are unknown. 



Neither Erdmann nor M°Murrich found generative organs in the five species 

 of Palythoa (" Corticifera ") examined by them. We have been more fortunate, 

 since in P. kochii we found male organs alone, and in P. howesii we found only 

 female. 



According to our experience all the members of a single colony of dioecious 

 Zoantheae belong to the same sex ; but we cannot lay down any general rule on 

 this point. 



Ccenencliyme. — The structure of the coenenchyme is similar in every respect to 

 that of the polyps. The only difference consists in the presence of coelenteric 

 canals, which are merely prolongations of the coelenteron of the polyps. 



