ANATOMY OP MUSSA AND EUPHTLLIA. 29 



fuller account of them in a future communication. At present 

 I will confine myself to a description of what I have seen. 



There are no directive mesenteries, Euphyllia agreeing in 

 this respect with Lophohelia and Mussa. Their absence is a 

 striking and important fact, adding as it does another type of 

 mesenterial arrangement to those we know already. We have 

 the normal Actinian arrangement, giving a bilateral symmetry 

 along the long axis of the stomodseum, the Edwardsian and 

 Alcyonarian arrangements in which the bilateral symmetry is 

 marked equally well, but in a different manner. The arrange- 

 ment in Zoanthus is clearly nothing more than a modification 

 of the Actinian type, and the arrangement in Cerianthus is 

 probably connected with an atrophy of the longitudinal muscles 

 in the same type. 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 

 polypes can be derived by fissiparity from one with directives, 

 and yet the arrangement of directives be carried over into the 

 daughter polyps, especially when an examination of an Astrseid 

 colony reveals the fact that the calices are constricted in their 

 centres at right angles to their long axes, and the long axes of 

 resulting calices may either be continuations of the long axis 

 of the original calyx, from which they were derived, or may be 

 set at right angles or any other angle to it. To state shortly 

 the extraordinary features in the remainder of the anatomy, 

 the stomodseum is very long, reaches nearly to the bottom of 

 the polyp, and is converted into a ramifying and inosculating 

 system of canals ; it functions as the chief digestive cavity of 

 the polyp. The endoderm is greatly vacuolated, and converted 

 into a reticulated tissue filling up the ccelenteron, in the 

 meshes of which are numerous nematocysts and symbiotic 

 algse. Mesenterial filaments are feebly developed on the 

 primary and secondary mesenteries, which are attached 

 throughout the greater part of their course to the stomo- 

 dseum, and do not reach a great development on the tertiary 

 mesenteries, which are free for the greater part of their course. 



