ANIMAL CHLOROPHYLL 879 



tion, to the blue corpuscles ; these finally become lodged in 

 the tunic, and in that way give rise to the surface pigmentation 

 of the animal. 



(b) Other Tunicates. 



There are many other ascidians in the Bermuda waters 

 which are highly coloured. In a cave on the west side of 

 Agar's Island ^ five specimens of the brilliant red tunicate, 

 Microcosmus miniatus, Verrill, were found. An 

 examination of the blood revealed that its most prominent 

 constituent was an amoeboid cell, containing many brilliant 

 carmine-coloured granules, which was very similar to the 

 pigment cell that colours the test. The animal from which 

 the blood had been extracted was examined on the day follow- 

 ing, and, as in A . a t r a , there were many intermediate stages 

 between the colourless cells and the pigmented corpuscles. 

 These observations confirmed in a substantial way those made 

 upon A . a t r a . 



Other species of ascidians have been examined and in every 

 case the colour of the pigment cells in the test was duplicated 

 by the coloured cells of the blood. The colonial form, E c t e i n - 

 ascidia turbinata, Herdman, which is brilliant orange in 

 colour, has as its only coloured cell in the blood-stream a 

 corpuscle possessing orange granules. 



(c) Discussion. 



Concerning the origin of the pigments in the blood-stream 

 of ascidians, no definite statement can be made. It has been 

 observed that the pigment cells arise while in circulation from 

 unpigmented corpuscles. Just what is the process involved 

 in that colour change it is difficult to explain. Grifiiths (1897) 

 has described a colourless respiratory proteid (y-achroglobin) 

 in the blood of ascidians, and the chromogen of Phallusia has 

 been stated by Henze (1911, 1912) to be a proteid in com- 

 bination with the element vanadium. It is possible, therefore, 

 that the change from the colourless cell to the ' chromocyte ' 



^ Where the laboratory is situated, 



