ANIMAL CHLOROPHYLL 349 



to the respiratory pigment. He found that in actinians which 

 were not infected with Zooxanthehae a respiratory pigment is 

 present, but that in forms which are ' packed with " yellow 

 cells " ' the pigment had ceased to perform a respiratory func- 

 tion. The most striking case which he observed was that of 

 Bunodes balli, in which occurs a facultative association 

 between itself and the Zooxanthehae : the larger variety of that 

 species has many Zooxanthehae and, as a result, is almost 

 without trace of any of the pigments common among other 

 forms ; the smaller variety of the same species is uninfected, 

 and as a result possesses a respiratory pigment. The results of 

 MacMunn's work are briefly as follows : (1) that a respiratory 

 pigment is present in most actinians ; (2) the pigment is not 

 a carrier of oxygen, but serves simply to store oxygen in the 

 tissue which is subsequently to use it ; (3) in those actinians 

 in which yellow cells are present the chlorophyllous pigment 

 of these organisms seems to replace the respiratory pigment ; 

 (4) besides this respiratory substance there are other pigments 

 (such as Moseley's actiniochrome) which serve for decoration.^ 

 In a recent paper on Actinia equina and A n e m o n i a 

 sulcata Elmhirst and Sharpe (1920) record several observa- 

 tions which are not in agreement with those of MacMunn. 

 They find that the non-haematin pigment, instead of being 

 purely ornamental, produces oxygen, possibly by photo- 

 synthesis. However, they report the presence of Zooxan- 

 thehae and fail also to find any haematin derivative, which 

 accords with the results of MacMunn. In addition, these 

 authors hold that the intensity of colour in A . equina 

 varies with exposure to light, and the pigment, therefore, 

 functions as a light screen. Certain observations made in the 

 course of the present study support this latter conclusion ; 

 when A. bermudensis is kept in the dark (three days) 

 the animal loses its deep red tinge and acquires a brownish-red 

 shade. Conversely, if an individual is exposed to direct 

 sunlight, its colour changes to a brilliant carmine. 



1 Quoted also by Griffiths (1892) ; an excellent description of MacMunn's 

 work will be found in Griffiths' book, especially in Chapter VIII. 



