THE ANATOMY OF ALOYONIUM DIGITATUM. 343 



The Anatomy of Alcyonium digitatum. 



By 



Sydney J. Hickson, M.A., D.Sc, 



Beyer Professor of Zoology in the Owens College, Manchester ; I'ellow of 

 Downing College, Cambridge. 



With Plates 36—39. 



Index of Contents. 



PAGE 



Preface ........ 344 



Section I. — History of our Knowledge of the Anatomy of 



Alcyonium ...... 344 



Section IT. — General Form and Natural History of the Colony 349 

 Shape — Size — Colour — Expansion and contraction of the polyps 

 — Contraction of the colony as a whole — Sexuality — Geo- 

 graphical and bathymetrical distribution — English species 

 of Alcyonium. 



Section III. — General Anatomy ..... 354 



The composition of the colony — The individual polyps and the 



colony — The appearance of the extensible portion — Size — 



Tentacles — Mouth — Disc — Stomodseum — Mesenteries — 



. ^ Ventral mesenterial filaments — Dorsal mesenterial filaments 



_ , — Gonads — Communication between individual polyps — 



The endodermic canals — Distribution of the spicules. 



Section IV. — Minute Anatomy ..... 363 

 The ectoderm — Nematocysts — Stomodseum — Mesenterial fila- 

 ments — Mesoglcea — Spicules — Endoderm — Ovaries and 

 testes — The buds. 



Section "V. — Notes on the Circulation of the Fluids in the 



Colony and the Digestion . . . 380 



VOL. 37, PAET 4. NEW SER. A A 



