II 



ALCYONIUM 



109 



in such a way as to produce an upward current of water towards the 

 stomodaeum. In the case of the six other mesenteries the mesenterial 



Ml- 



m. 



ay. 



B 



Fig. 47. 

 Alcyoniunt'. transverse sections. A, through stomodaeum; B, slightly below stomodaeum. 

 eg, Ciliated groove ; M, mesenteries ; m, muscle ; M.f, mesenterial filament ; s, stomodaeum. 



filament is much folded, forming a little skein-like mass ; it extends 

 only for a short distance down the free edge of the mesentery and 

 its epithelial covering is 



crowded with gland-cells, .^,ii:--rV''''i'^i'^^- coel. 



which secrete the diges- 

 tive ferment. Below 

 the level of the mesen- 

 terial filaments these six 

 mesenteries show during 

 the winter months little 

 rounded swellings near 

 their free edge. These 

 swellings are the young 

 ovaries or testes, which 

 are consequently endo- 

 dermal inpesitionasthey 

 are in the Acalephaie. 



The ectoderm covers 

 the outer surface of the 

 polyp and of the colony 

 in general : the endo- 

 derm lines the coelen- 

 teric spaces. Between the two layers of cells are extensive regions filled 



sp. 



Fig. 48. 

 Portion of section through Alcyonium colony parallel to 

 surface, coel, Coelenteron with the eight mesenteries, the two 

 dorsal ones showing mesenterial filaments (black) ; sp, spicules ; 

 si, strands and t, tubes of endodenn connecting the walls of the, 

 various coelentera. The dotted groundwork of the figure repre- 

 sents the matrix of mesogloea. 



