NOTE ON THE MESENTERIES OF ACTINIANS. 551 



Note on the Mesenteries of Actinians. 



By 



A. Frasei* Dixon, 



Royal College of Science, Dublin. 



In a paper published in the last number of the ' Quarterly 

 Journal of Microscopical Science' (193, January, 1894) on 

 "Octineon Lindahli/' the author, Dr. G. H. Fowler, gives 

 a figure — woodcut Fig. A, — and as my name is given in con- 

 nection with it, perhaps I may be allowed to make a statement 

 regarding it. The figure " represents Sagartia, Actinia, 

 Bunodes (Lacaze-Duthiers, corroborated by F. Dixon)." Some 

 time ago Professor Haddon, who was then writing the first 

 part of his " E-evision of British Actinise," asked me to cut 

 sections of young specimens belonging to the genera whose 

 development Lacaze-Duthiers had described. He asked me to 

 do this because the Hertwigs, from their observations on 

 Adamsia diaphana, assumed that Lacaze-Duthiers had 

 made a mistake in determining which were the first eight 

 mesenteries to arise in Sagartia, Actinia, and Bunodes. They 

 assumed that in these genera, just as in Adamsia diaphana, 

 the most " ventral " of the dotted mesenteries in Fig. A of Dr. 

 Fowler was developed so early as to form one of the eight 

 mesenteries in the stage with eight mesenteries. If this were 

 so the eight-mesentery stage in Sagartia, Actinia, and Bunodes 

 could not correspond to the permanent condition in Edwardsia, 

 or to the condition described first by Professor Haddon for the 

 larva of Halcampa, because in these no " lateral " mesentery is 

 present with its muscle plate pointing " dorsal wards." The 

 Hertwigs' figure for Adamsia is given by Dr. Fowler in Fig. B, 

 and this represents what they assumed to be the arrangement 

 also in young specimens of Sagartia, Actinia, and Bunodes. 



