134 Scientific Proceedings, Royal Dublin Society. 



pi. sii. figs. 28, 31) also shows that in Edwardsia the mesenteries 

 appear in this order, " ventro-lateral," " dorso-lateral," " ventral " 

 and " dorsal." 



The only account we have of the structure of Euphyllia is that 

 by Bourne (1888). He says : " There are no directive mesenteries, 

 Euphyllia agreeing in this respect with Lophohelia and Mussa. 

 Their absence is a striking fact, adding as it does another type 

 of mesenterial arrangement to those we know already." After 

 alluding to the arrangement of the mesenteries in the normal 

 Actiniae, Edwardsia, Alcyonaria, Zoanthus and Cerianthus, he goes 

 on to say — " All these forms show a bilateral symmetry ; Mussa, 

 Lophohelia, and Euphyllia alone are perfectly radial. This may 

 either be a primitive condition or may be connected with fissiparity, 

 for it is impossible to conceive how two polyps can be derived by 

 fissiparity from one with directives, yet the arrangement of direc- 

 tives may be carried over into the daughter polyps." Our larva 

 proves that Euphyllia, at all events, is primitively bilaterally sym- 

 metrical ; those Actiniae which give rise to new individuals by 

 fission are characterized by absence of directives or by irregularity 

 in their number and position — a feature which we must now 

 regard as secondary. The stomatodeeum shows no indication in the 

 larva of the great and complex development which characterizes 

 the adult Euphyllia. 



Finally, I would like to direct the reader's attention to a Paper 

 recently published by van Beneden (1890), in which he describes a 

 larval Zoantharian which is evidently allied to " Semper's larva " 

 (1867). Van Beneden's larva is in the same stage as that described 

 in the present communication, and as in Euphyllia the sulcular 

 directives are short and do not bear mesenterial filaments, the 

 difference being that in the former these mesenteries are imperfect, 

 i. e. they do not reach the stomatodeeum. The mesogloea also 

 contains cellular elements, apparently derived both from the ecto- 

 derm and the endoderm. Taking these two facts into account van 

 Beneden not unnaturally suggests that his larva (and probably 

 also, Semper's) may be a stage in the development of a microtypal 

 Zoanthean. Personally I regard the eellullar inclusions in the 

 mesogloea as being a more important argument than the character 

 of the mesenteries, as these appear to differ but slightly from those 

 I have just described. In a yet more recent Paper (1891), van 



