402 
themselves into the developmental cycle of other organisms, 
it will not, perhaps, appear to be over rash if we raise the 
question whether, indeed, these Yellow Cells are to be con- 
sidered at all as integral parts of the Radiolarian body? As 
a matter of course, developmental studies alone can bring 
light here. 
In the first attempt to follow the origination of the Yellow 
Cells in the protoplasm, the observation did not appear to be 
encumbered by any serious difficulty. As is known, the 
Yellow Cells multiply by division, and one finds them of 
various sizes. Easy also is it to find in the body of the 
Radiolarian examined, naked, yeilow-coloured, protoplasmic 
specks, which one would feel inclined to regard as the first 
steps in the development of a Yellow Cell. It has turned 
out, however, from more careful observations, that the par- 
ticular Radiolarian observed .had taken in as food yellow 
Tintinnoids, and that the yellow colour of the protoplasmic 
specks arose from the undigested food. I failed to discover 
any single fact which proved the direct origin of the Yellow 
Cells from the protoplasm of the Radiolaria. In order to 
get nearer to the question in another way, I availed myself 
of the interesting fact discovered by Schneider, that the Cap- 
sule of Thalassicolla, when extruded from its shell, had the 
power of building up anew the Radiolarian body. I thought 
in this way to be able to follow the formation of the Yellow 
Cell step by step, and the more so since Schneider succeeded 
in nursing the regenerated Thalassicolla up to the point of 
development of Yellow Cells. In my researches, which 
I also carried on with Thalassicolla nucleata (the blue 
coloured variety), the extruded capsules certainly did go so 
far as to produce new pseudopodia coloured with blue par- 
ticles, only I had not the luck fully to follow out the process 
of regeneration. The only new fact which I have found 
relating to the Yellow Cells is this, that in Collozoum which 
for some time lay in sea water (over a week), the Yellow 
Cells proceeded gaily to grow even when the protoplasm and 
capsules of the whole colony were already completely decom- 
posed. In this condition there appeared around the Yellow 
Cell a somewhat tough viscid membrane, which completely 
enclosed it (figs. 25, 26h). From this sheath the growing 
cells escaped very slowly, forming a new envelope which in 
turn became discarded also. This formation of a sheath 
occurred in the same cell several times ; the escape from the 
sheath took place so slowly that it was not possible to observe 
it directly. The liberated cell grew, acquired a ragged 
outline, and multiplied itself finally by division This pro- 
