32 GILBERT 0. BOURNE. 



long been known in Hydroids, but has not previously been 

 described for the Anthozoa. The cells of the mesenterial 

 filaments are vacuolated, but their boundaries are clearly 

 recognisable. 



The structure of Euphyllia as above described is without 

 parallel in the Madreporaria, or indeed in the Anthozoa, the 

 ramified digestive tract and parenchymatous tissue suggest a 

 comparison with Dendroccele planarians; but the com- 

 parison will not hold good for a moment when we consider that 

 the alimentary tract of the latter is formed from hypoblast, whilst 

 that of Euphyllia, formed by the stomodseum, is ectodermic. 



Any attempt to explain such isolated phenomena as these 

 must be peculiarly liable to error, but possibly the following 

 explanation may throw some light on the peculiarities. The 

 endoderm of Euphyllia as of most Madreporaria is filled with 

 symbiotic algse. These contribute an important share towards 

 the nutrition of the polyp, and it is conceivable that the 

 symbiotic nutrition, if one may express it so, became of such 

 primary importance to the economy of the animal that the 

 endoderm lost its original digestive function and became vacuolar 

 in order to accommodate greater numbers of zooxanthellse. 

 A comparison between the vacuolated endoderm of Euphyllia 

 and the extracapsular protoplasm of the Radiolaria, will explain 

 my meaning. In both cases the vacuolation is probably con- 

 nected with the presence of zooxanthellse. The ectoderm is 

 known to retain the power of amoeboid digestion in many 

 Ccelenterata, including Actinia mesembryanthemum and 

 Bunodes sabelloides (Metschnikoff, f Researches on the 

 Intracellular Digestion of Invertebrates/ this Journal, new 

 ser., xxiv, p. 93). There is nothing surprising then that at the 

 same time that the endoderm became modified in connection 

 with symbiosis, that the ectoderm of the stomodasum should 

 have taken a more active part in alimentation, and that its 

 surface should be greatly increased to meet the remaining 

 necessities of the organism. 



It has long been felt that a classification of Madreporarian 



