PHYSIOLOGY OF ASCIDIA ATRA LESUEUR 233 
It was not difficult to satisfy the first of these requirements. 
The blood contains cells whose volume is the same as that 
occupied by the compact group of pigment bodies. In addition, 
these blood cells are packed full of spherical granules whose size 
and number correspond to the pigment granules in the test. 
Most of the blood cells are of a rich green appearance, the color 
being resident in the granules. There are also to be found, in 
much less abundance, similar blood cells whose granules instead 
of being a transparent green, are an opaque, dark blue, which 
to all appearances is identical with the color of the test. It was 
possible to observe the change from green to blue in individual 
cells in drawn blood under the microscope. I considered it, 
therefore, extremely likely that the blue blood cells, representing 
the later stages of the green cells, are the forerunners of the groups 
of pigment granules in the test. 
In order to prove this satisfactorily, it was necessary to find 
a stage between the free, blue cell and the group of pigment gran- 
ules imbedded in the cellulose of the test. Examination of 
sections of the test brought out only a few, and these doubtful, 
instances, indicating that pigment deposition in an adult Ascidia 
is probably not a very active process. 
The evidence came when it was found that an animal would 
regenerate its test. An individual denuded of a portion of tbe 
test began almost at once to secrete a new one. At the end of 
one day, a thin layer of cellulose of the characteristic color had 
been formed over the denuded portion. When this delicate 
layer was removed and examined with the microscope, there 
were found hundreds of definitely shaped, blue blood cells 
imbedded in the cellulose, imparting to it the usual color of the 
test. Asa result of this, it seems safe to conclude that the blue 
pigment granules in the test of Ascidia are the remains of the 
metamorphosed green cells of the blood. 
In this connection the observations of Caullery (95) are of 
interest. Botrylloides cyanescens, which in nature is yellowish 
green, turns blue after remaining in the laboratory. Caullery 
found that the green color was due to cells which contained a 
number of colored granules, and that the blue appearance in 
