480 



Dr. J. S. Thomson on living Gorgon/as 



much paler in colour, and on the other hand there are 

 examples of Gorgonia verrucosa which have yellowish or 

 slightly reddish tints. Von Koch also mentions tlie occur- 

 rence of a yellowisi)-red specimen of Gorgonia cavoUni. 



This instability of the colouring is met with in otlier 

 Alcyonavian forms, and perhaps it is most conspicuously 

 illustrated in Alcgonhim purpureum, Hickson, occuning in 

 False Bay at the Cape of Good Hope. Akyonium pur- 

 pureum is a brilliant purple colour (not due to the spicules), 

 which it has been found almost impossible to retain by 

 different methods of preservation. 



The colour of Alcyonarians has within recent years been 

 recognized as being so variable in character that it is 

 no longer regarded as of importance in the determination of 

 species. 



After an examination of a number of the red form 

 {^Gorgonia cavolini) and of the wliite form {Gorgonia verru- 

 cosa) it appears to me that none of the characters which 

 von Koch gives for tlieir differentiation into two species 

 will hold in all cases. The characters by which von Koch 

 separates Gorgonia cavolini from Gorgonia verrucosa are as 

 follows : — 



Gorgonia verrucosa, Pall. | Gorgonia cavolitii, v. Koch. 



The colonies are white during Are red or reddish during life, 



life. 



The colonies are, as a rule, of larger 

 size, 



The branching is rarely in one 

 plane and is irregular. 



The branches are longer and less 

 divided up into minor branches. 

 The branches frequently appear 

 little thinner than the stem, and 

 often have a tendency to lie 

 parallel to one another, and 

 perpendicular to the basal plane 

 of attachment. 



The polyps are yellowish or light 

 brown. 



The polyps are not arranged in 

 rows on the twigs. 



The polyps have the margins of 

 the calyces divided up into 

 .5-8 lobes, but usually into 8. 



Yellow cells occur in the ectoderm 

 of the tentacles. 



white when dried or preserved 

 in alcohol. 



The branching is in one plane and 

 more regular. 



The branches are shorter and fairly 

 uniform: the twigs are little 

 thinner than the branches and 

 always disposed in one plane. 



The polyps are reddish. 



The polyps are arranged in rows 

 ^on the twigs. 



The margins of the calyces are 

 usually 5-lobed. 



Yellow cells do not occur in the 

 ectoderm of the tentncles. 



4 



