Observations on living Oorgonias. 479 



LIX. — Observations on living Qorgonias (Gorgonia verru- 

 cosa) occurring in the English Channel. By J. Stuart 

 Thomson, Ph.D., F.L.S., F.R.S.E., Lecturer and Senior 

 Demonstrator \n Zoology, Victoria University of 

 Manchester. 



During a brief period of work at the Marine Biological 

 Station, Roscoff, in August 1912, I had excellent opportunities 

 of observing the variations in the form of Gorgonia verru- 

 cosa^ Pall., from living specimens, and of comparing the 

 latter with the form designated Gorgonia caboHni, von 

 Koch. 



These two forms, sometimes called Sea-fans, are the 

 commonest Gorgonacete occurring in the Gulf of Naples, the 

 Gulf of Lyons, and in the English (Jhanne}, off the coasts of 

 Brittany, Devonshire, and Cornwall. 



In 1887, von Koch in his admirable Monograph on the 

 Gorgonidae of the Gulf of Naples, gives a detailed account 

 of the anatomy and development of a red Gorgonia under 

 the name Gorgonia cavolini, sp. n., which he regards as 

 very similar to, but not identical with, Gorgonia verrucosa. 

 Pall. Von Koch holds that naturalists had, hitherto, fre- 

 quently erred in regarding these t^yo forms as belonging to 

 the same species. He rightly insists that one should observe 

 as many forms as possible before arriving at conclusions as 

 to their identification. 



The object of this note is mainly to state my reasons for 

 regarding Gorgonia veri-ucosa, Pall., and Gorgonia cavolini, 

 von Koch, as one and the same species. It is of importance 

 in the determination of species that specimens from different 

 localities should be compared with one another; and my 

 present note is of importance in this connection, as 

 von Koch's work was based on Mediterranean forms, but my 

 observations are on specimens from the western part of the 

 English Channel, namely from the coasts of Brittany. It is 

 also almost necessary in some difficult or disputable cases 

 that Alcyonarian forms should be studied \\\ the living 

 state. 



The first character upon which von Koeli rests his deter- 

 mination is the colour — Qorgoniu cavolini being red, Gor- 

 gonia verrucosa white. When these two forms are dead or 

 preserved in spirit, they are both white and are practically 

 indistinguishable. The colour of the red foru), Gorgonia 

 cavolini, is very unstable, disappearing very readily and 

 rapidly, and the pigment is not present in tlie spicules. 

 The red colour of Gorgonia cavolini also varies in shade in 

 different specimens even in the living state ; thus 1 find some 



