Compound Ascidian Diazona violacea, Savigny. 231 



Sorby, changed to purple when strongly acidified, but regained its original 

 shade on neutralisation. 



From all the above observations it must be concluded that the green 

 colour of Diazona probably results from some chlorophyll-like body. Though 

 the spectra are not exactly those of ordinary plant chlorophyll there is quite 

 a resemblance, and the association of separable green and yellow pigments 

 from the alcoholic solution is also very suggestive. 



If it is a chlorophyll body one is driven to the view that the green colour 

 arises from a symbiotic alga, as chlorophyll does not appear to be a likely 

 pigment for a marine animal. In a monograph on the compound Ascidian 

 Fragaroides aurantiacum, by Charles Maurice,* the' pigmentation of the test 

 is described, and the author concludes that there the yellow pigment cells 

 are in reality algae (a Protococcus), which contain chlorophyll. He comments 

 on the fact that these algee when free show colours ranging from green to 

 yellow, and that their cells during the period of reproduction resemble most 

 closely the colour and structure of the globules in the test of the Ascidian. 

 There are, however, three possible objections to this view. Firstly, Diazona 

 has been collected from a depth of 60 fathoms, and it would appear to be 

 most improbable that sufficient actinic light would penetrate to that depth 

 to cause the formation of chlorophyll. Secondly, there is the evidence of 

 Pizonf that in certain Tunicata which show very similar pigment cells to 

 those of Diazona the yellow or yellow-green pigments result from the waste 

 products of the organism, and are gradually excreted from its surface. Chloro- 

 phyll would hardly be a waste product. Thirdly, the pigment cells in Diazona 

 are far smaller than the algal cells in known cases of symbiosis. The cells 

 appear as minute spheres filled with one or more drops of an oily substance 

 (judging by their high refractive index), and do not appear to show the 

 structure of an algal cell. Until it is possible to work with some fresh, 

 living colonies of Diazona, nothing more definite concerning the green 

 pigment can be said than that it resembles chlorophyll in many respects, 

 but is not identical with that ordinarily obtained from plants. It is, 

 however, more like chlorophyll than the green pigment obtained by Sorby 

 from Bonellia, and possibly represents algal cells. 



Extraction with alcohol having shown that the purple pigment was all 

 but insoluble, some 400 grm. of the organism were worked up on the lines 

 employed by Friedlander in the case of the Mollusc Murex hrandaris.i 



The material was first ground with sand and then digested for several 



* ' Arch, de Biol.,' Li6ge, 1888. 



t 'Compt. Kend.,' 1899, p. 395, and 1901, p. 170. 



% ' Ber.,' 1909, p. 765. 



/ 



