128 



Scientific Proceedings, Royal Dublin Society. 



that wHoh I have described (1889, pp. 352, 354), as the fourth stage 

 of mesenterial development. 



A few years ago (1887, p. 479) I drew attention to the impor- 

 tance of this stage in the development of Halcampa, and the 

 following year I described it in Peachia (1888, p. 256). 



McMurrich (1889, p. 31) has also found this stage in the 

 development of Aulactinia stelloides, and has also drawn attention 

 to its " Edwardsian " character ; but Lacaze-Duthiers was the 

 first to observe it, though he did not discuss its significance. 



In describing larvse at this stage it is necessary to have a 

 consistent system of terminology, and until it is replaced by a 

 better I shall adhere to that which I introduced in my " Revision 

 of the British Actiniae." I there proposed " sulcus " for the 

 "ventral," and " sulculus " for the "dorsal" grooves. The 

 former is the more important groove : it is that which is so marked 

 in Peachia and which alone occurs in the Zoanthese. In those 

 adult Actiniae which possess but a single groove it is not, however, 

 always possible to determine whether this is sulcar or sulcular. 



Fowler's terms of " endocoele " for an intramesenterial 

 chamber, and " exoccele " for an intermesenterial chamber are so 

 appropriate that they are sure to be universally adopted. Hertwig's 

 employment of the term " directive " for the pairs of sagittal 

 mesenteries is also very happy. 



The foregoing diagram illustrates the method of naming the 

 mesenteries and chambers which I have adopted. 



