26 



ACTINIARIA 



tentacles contains nematocysts as well as spirocysts. The longitudinal muscles of the tentacles are always 

 ectodermal as are also the radial muscles of the oral disc. The actinopharynx is longitudinally sulcated. In 

 no'casel have observed any dorsal siphonoglyphe ; on the other hand, I have in representatives of all four genera 

 found a ventral siphonoglyphe, a little developed. It it distinguishable from the other furrows of the actino- 

 pharynx through its cells being provided with longer cilia than those of the other part of the actinopharynx 

 (Textiig. 7, 8). The ectoderm of the actinopharynx contains nematocysts, sometimes of two kinds. 



The mesenteries are partly perfect, provided with reproductive organs, longitudinal pennons and 

 filaments, partly imperfect without such organs, and only present in the uppermost part of the column. The 

 former, "the Edwardsia-mesentenes" , are arranged as the diagnosis indicates. There are thus 2 pairs of direc- 

 tive mesenteries and 2 couples of lateral mesenteries, the latter forming pairs with 4 imperfect mesenteries 

 (textfig. 9). In the simplest case there are only 4 imperfect mesenteries developed, belonging to the first 

 order, as in E. andresi (textfig. 9). In most species a more or less imperfect cycle of the second order is added, 

 and sometimes one of the third order. The longitudinal muscles of the perfect mesenteries always form 

 pennons with more or less numerous folds. The pennons are always distinctly distinguishable from the other 

 part of the mesenteries, but seem never to be circumscript in the sense that the inner and outer lamellar parts 

 of the mesenteries issue from one point of the fold or very close by each other. 



The outer lamellar part of the mesenteries is in the reproductive tract attached to the pennon near 

 its outer edge or somewhat nearer to the middle of it. At the insertions of the mesenteries on the colunm 

 the perfect mesenteries have developed the so-called parietal muscles ; one part of these is placed at the same 

 side as the pennons and is only a differentiation of the longitudinal muscles, the second part, arranged at the 

 opposite side of the mesenteries, is homologous with the parietobasilar muscles in the more differentiated 

 Actiniaria (Carlgren 1905). The parietal muscles also show a different appearance in several species, com- 

 monly extending, and as a rule without folding, over a smaller or greater part of the column, whereby the 

 contraction of the body in longitudinal direction is facilitated. In exceptional cases, as in Milne-edwardsia 

 nathorstii, these column-muscles are comparatively strong and form rather high folds (textfig. 85) . Towards 

 the aboral end of the body the longitudinal pennons taper more and more and end by fusing with the outer 



ers are namely of another colour than the other part of the disc. Bourne supposes that the development of the micro-mesen- 

 teries in the Edwardsids is another than in the other Actiniaria and will not regard the mesenteries 9 — 12 and the other micro- 

 mesenteries as homologous with those on the Actiniaria. In comparing the mesenteries as homologous with those of for instance 

 Halcampa (Carlgren 1893 a textfig. 0. i a) I cannot find any difference. The arrangement of the mesenteries in E. claparedii 

 and in other Edwardsia having 16 tentacles agrees for instance with that in Gonaciinia and in a young specimen of Sagartia (Cy- 

 lisla) undata (Carlgren 1893 a p. 99). Bourne's statement that the micro-mesenteries in Edwardsia arise in couples of singles, 

 and not in couples of pairs as in the Actiniaria, certainly needs a more extensive examination before it can be accepted. I 

 think that the development of the tentacles is mainly the same in the Edwardsids and in the other Actininae. As namely, by the 

 appearance of a new pair of mesenteries in the Actiniaria, the new tentacles, one endocoel- and one exocoel-tentacle, do not arise 

 quite simultaneously, and as the foundation of the mesenteries agrees with that of the tentacles, it is clear that in certain stages 

 of development we miist iind single mesenteries instead of pairs. (Compare Bourne's statement Quart. Journ. Mic. Sc. 63 1919) 

 concerning the development of the mesenteries of Phellia. Also in the paper by Faurot (1905) in which he describes the devel- 

 opment of the tentacles of Ilyanthus, we can in some figures see an indication of a different size of both mesenteries of the same 

 pair (that this is not always the case is probably an inadvertency of Faurot, to whom the principal object has evidently been 

 to investigate the order of appearance of the tentacles and not that of the mesenteries). Besides this, it ought to be remarked 

 that in several Actiniaria (in the Actinostolids, in some Halcuriidae as in Actinerniis and others) a great difference in both 

 mesenteries, belonging to a pair, exists. Thus Bourne's suggestion that the Edwardsiae should form a special group of the 

 Anthozoa, different from the Actiniaria, is, according to me, not well founded. 



