ANIMAL CHLOROPHYLL 377 



exceptionally large variety (ten distinct types) of blood-cells. 

 In the vascular fluid of this animal there are three kinds of 

 highly-pigmented cells : green, orange, and blue ; in addition 

 there are four kinds of non-motile white corpuscles, and three 

 other types which are distinctly amoeboid (Fulton, 1921 h). 

 The writer has shown that all of the pigmented cells in A . a t r a 

 arise directly in the blood-stream from unpigmented corpuscles. 

 In the case of the green ' chromocyte ' the metamorphosis from 

 the colourless cell may be stimulated artificially and the 

 complete process watched under the microscope. When an 

 acid, preferably an organic acid of N/10 to N/20 slirength, is 

 added to a fresh smear of blood, all the non-motile colourless 

 cells of one variety may be observed to take on a light shade of 

 green, which gradually deepens ; at the same time the cell 

 fragments into large green lumps and finally assumes the 

 characteristic form of the green pigment cell. Th(3refore, it 

 may be inferred that in nature the green pigment cell arises 

 from an unpigmented corpuscle as a result of an increase in 

 acidity. 



The orange and the blue cells also arise from unpigmented 

 corpuscles, but in a slightly different manner. Various methods 

 were employed in an effort artificially to stimulate the change 

 from the colourless to the orange and to the blue cells. No 

 response was secured from acids or bases, but it was observed 

 in smears of blood taken from an animal which previously had 

 been weakened by the loss of blood, that there occurred many 

 intermediate stages between the unpigmented corpuscles and 

 the orange cell or the blue cell. If one of the intermediate 

 stages be carefully watched, under very favourable conditions, 

 there is some indication that it gradually increases its depth cf 

 colour. With this evidence ^ the conclusion is unavoidable that 

 all of the pigmented cells arise in the blood-stream directly 

 from colourless ones. 



The deep purple-blue colour of the tunic of A . a t r a is 



^ The details of the experiments and a more complete statement of the 

 evidence for this conclusion will be found in the paper by Fulton (1921 b) 

 on the blood of Ascidia atra. 



D d 2 



