378 JOHN F. FULTON, JR. 



caused by th(! presence of large blue pigment cells (H(icht, 

 1918 a; Crozier, 1916 rf) containing spherical granules, which 

 migrate from one part of the cell to another. The blue cor- 

 puscles of the blood-stream are like the pigment cells of the test 

 in every detail of their structure. It remains, therefore, to 

 establish the identity of these cells. In the first place, the 

 presence in botii cells of a very prominent vacuole is strong 

 evidence in favour of their being identical. In testing the 

 cells with various reagents another interesting resemblance 

 was noted. It is known that calcium chloride in miimte 

 amounts has the power of greatly acceleratijig the activity of 

 phagocytes (Hamburger, 1910 and 1916) ; it also causes 

 a decided increase in the activity of the blue pigment cells 

 both of the blood-stream and of the test. After a M/10 solution 

 of CaCla has been added to a fresh smear of blood the blue cells, 

 which in their quiescent state are nearly spherical, inmiediately 

 send forth pseudopodia, and at the same time the blue granules 

 within the corpuscles commence to move from one end of the 

 cell to the other. In the test, however, the pigment cells, 

 inasmuch as they are fixed within the substance of the test, 

 cannot move their processes ; there is, nevertheless, following 

 the addition of CaOla to a section of the test, a decided 

 activity on the part of the blue granules,-^ an activity which 

 is similar to that displayed by the corresponding granules 

 of the blood-cells. The conclusion, therefore, seems to be 

 warranted that the two cells are identical, and consequently 

 that the blue cells in the blood give rise to the pigment cells 

 of the test.^ 



From these two kinds of evidence it is a reasonable conclusion 

 that in Ascidia atra the coloration of the animal is even- 

 tually traceable to the colourless cells of the blood ; for, as has 

 been shown, the unpigmented cells give rise^ while in circula- 



1 A description of a phenomenon of this kind is also to be found in 

 Pizon's (1898, 1901) papers on the pigment granules of tunicates. 



^ Hecht (1918 «) states that when A. atra regenerates a portion of 

 its test, there are a great many of the blue blood-cells in the area of the 

 regenerating tissue. 



