338 COELENTERATA ANTHOZOA chap. 



symbiotic "Algae" (cf. p. 2G1) they carry. A diffuse salmon- 

 pink colour soluble in spirit occurs in the living Primnoa lepadi- 

 fera of the Norwegian fjords, and a similar but paler pink colour 

 occurs in some varieties of the common Alcyoniuni digitahim. 

 Gilchrist ^ states that when he was preserving specimens of 

 Alcyonium jmrpureum from Cape waters a considerable quantity 

 of a soluble purple pigment escaped. 



But the predominant colour of Alcyonarians is usually due 

 to the insoluble pigments of the calcareous spicules. These 

 may be of varying shades of purple, red, orange, and yellow. 

 The colours may be constant for a species or genus, or they may 

 vary in different specimens of one species, or even in different 

 parts of a single colony. Thus the skeletons of Tuhijyora musica 

 from all parts of the world have a red colour, the species of the 

 genus Anthomastus have always red spicules. On the other 

 hand, we find in Melitodes dichotoma red and yellow varieties in 

 the same locality, and in M. chamaeleon some of the branches 

 of a colony are red and others yellow. In Ghironephthya 

 variabilis the colour of the spicules in any one specimen varies 

 considerably, but in a collection of several specimens from a single 

 locality a kaleidoscopic play of colours may be seen, no two 

 specimens being exactly *the same in the arrangement of their 

 colour pattern. The influences that determine the colour of the 

 spicules is at present quite unknown, and in view of the great 

 variability that occurs in this respect, colour must be regarded as 

 a most uncertain guide for the determination of species. The 

 blue colour of the genus Heliopora is due to a peculiar pigment 

 which shows characteristic bands in the spectrum.''^ 



Phosphorescence. — A great many Alcyonaria are known to 

 be phosphorescent. Moseley says that " All the Alcyonarians 

 dredged by the ' Challenger ' in deep water were found to be 

 brilliantly phosphorescent when brought to the surface." The 

 phosphorescence of the common British Pennatula j)hos2)horea 

 has attracted more attention than that of any other species, 

 and has been well described by Panceri, Forbes, and others. 

 Porbes ^ says, " The pen is phosphorescent only when irritated by 

 touch ; the phosphorescence appears at the place touched, and 



^ Quoted by Hickson, Marine Investigations, S. Africa, iii. 1904, p. 215. 



- G. C. Bourne, Phil. Trans. Eoy. Soc. cLxxxvi. 1895, B. p. 464. 



^ Quoted by Marshall, Ohan PcnnatuUda, 1882, p. 49. 



