YELLOW-BROWN CELLS OF CONVOLUTA PARADOXA. 453 
(d) The Fate of the Yellow-brown Cells.—The 
yellow-brown cells persist throughout the normal life of C. 
paradoxa. Comparatively few in the very young, the 
number increases with the size of the animal. A casual 
observer, noting this large number of cells in the body of the 
adult, many of them of great size and many undergoing 
division, would be tempted to conclude that the yellow-brown 
cells were living parasitically upon the animal. 
The evidence just given, together with that which follows, 
demonstrates that this way of looking at the relationship 
between C. paradoxa and its yellow-brown cells is erroneous. 
For, beside the tribute of fat which it exacts regularly from 
the algal cells, the animal has another and more drastic mode 
of exploiting them. 
If animals are kept in darkness in sea-water filtered 
through a Pasteur-Chamberland filter, they exhibit, of course, 
starvation phenomena and become reduced greatly in size. 
This reduction in size is greater, and takes place much more — 
rapidly in such dark-kept than in light-kept animals. 
Thus animals of the same history were put in filtered sea- 
water on August 29th, 1907, and kept some in light and 
some in darkness, ' After nine days the light-kept animals 
were recognisably less reduced in size than the dark-kept. 
Measurements gave, in divisions of the Leitz ocular micro- 
meter, oc. 2, obj. 3 (= L. 2. 38) 140 x 60 = 8400 in the case 
of a light-kept: 75 x 44= 3300 in that of a dark-kept 
animal. That is the area of the former measured 142 sq. mm., 
the area of the latter 56 sq. mm., or 24 times less, 
The experiment, which was repeated frequently in the 
course of this research, demonstrates that, in the light, sup- 
ples are forthcoming from yellow-brown cell to animal, and 
that, in the dark, such supphes are either altogether lacking 
or much smaller in amount. In other words, the experiment 
confirms the previous conclusion that the yellow-brown cells 
are the seat of photosynthetic activity, and that products of 
this activity pass from algal cell to animal tissue. 
