COLOUR VARIATIONS IN ACTINIAE. 22& 



the varieties are so well marked as to have been considered distinct 

 species at various times. 



While working at Aberystwyth, in Wales, I was struck, while 

 collecting, by the fact that light had a great deal to do with the distri- 

 bution of the variously coloured forms, those from exposed positions 

 being dark red, etc., while those from under stones, or seaweed, or from 

 caves, were mostly of light shades, or green. This has also been 

 recorded for another member of the genus, Actinia tenebrosa, Farquhar^ 

 from Xew Zealand. In describing this species the author says : " This 

 Is the southern representative of the European species A. equina" etc. 

 " This species is a good example of the effects of light on the colours of 

 animals. Full-grown individuals, in situations well exposed to the rays 

 of the sun, have the column greenish, or brownish black, and the disk 

 and tentacles dusky crimson, while those on the under side of over- 

 hanging stones are reddish brown or crimson, the depth of colour 

 varying according to the amount of light that reaches them. Specimens 

 on the vertical sides of rocks (their favourite habitat) often have a 

 patch of reddish brown on the side turned away from the light. I 

 found a specimen under a large stone which had evidently never been, 

 in the light : the whole animal was yellowish white with a slightly 

 greenish tinge." 



No remarks are made as to any variation in the size, number, or 

 colour of the acrorhagi, or '■■ marginal spherules." 



Investigation of Aberystwyth specimens of A. equina showed that a 

 correlation exists between environment and these organs, which are as 

 a rule of a bright blue. M. Haime (quoted by Gosse) gives the follow- 

 ing table of number of spherules : — 



18 if 5th cycle of tentacles not developed. 

 24 if 5 or 5 J cycles are developed. 

 48 if 6 cycles are developed. 



My observations on some hundreds of specimens prove this to be 

 correct if an average be taken — in effect there are considerable differ- 

 ences. Those individuals which are of dark shades and occur in • 

 exposed positions, tend to possess more acrorhagi than those which live 

 in sheltered situations and which are of paler shades. In these last 

 also the acrorhagi are fewer, smaller, and of a pale blue, whilst in the 

 darker specimens the acrorhagi are larger, of a much deeper blue, and 

 often irregular (bilobed, etc.) in form. The colour of the acrorhagi 

 (lighter and darker) is of course due to the same circumstances that 

 cause the colour differences in the rest of the individual ; but the 

 variation in size is not necessarily due to this cause, and in all proba- 



