12 



THE ANTHOZOA 



we find dimorphism occurring in individual species of many 

 families which in other respects are widely separated from one 

 another. Only in one group, the Pennatulacea, is dimorphism of 

 constant occurrence. 



Much attention has been paid to the skeleton of the Alcyon- 



Fio. IV. 



1. Transverse section through the stomodaeum of Funiculina quadrangularis. sc, sulcus. 



2. Transverse section of the same species below the level of the stomodaeum. scm, sulcar 

 mesenteries ; ascm, asulcar mesenteries. 



3. Longitudinal section of a tentacle of Alcyonium digitatum. ec, ectoderm with ectodennic 

 nerve plexus ; mg, mesogloea ; en, endoderm. 



4. Transverse section through a portion of a mesentery of Alcyonium digitatum, showing 

 the large retractor muscle fibres borne on branched processes of the mesogloea, and the delicate 

 protractor muscles on the opposite face of the mesentery. 



5. Transverse section through one of the sulcar mesenterial filaments of Alcyonium digi- 

 tatum, showing the gland cells, gc, and the flagellate cells, fc. 



6. Transverse section through an asulcar filament of the same species, showing the open 

 groove lined by elongate ciliated ectoderm cells. 



7, 7a, 76, 7c, 7d. Myoepithelial cells from the endoderm of Alcyonium digitatum. 



8. Two nematocysts of Alcyonium digitatum. (1 and 2 original ; the rest after Hickson.) 



aria, but for taxonomic purposes it is of subordinate value. A 

 calcareous skeleton is present in all, with the exception of Proto- 

 caulon, Cornularia, some species of Clavularia, and Monoxenia, 

 and it is possible that spicules so minute as to have been over- 

 looked are present in these forms. The calcareous skeleton 



