YELLOW-BROWN CELLS OF CONVOLUTA PARADOXA. 451 
case when no other food is available. What seems to be con- 
clusive proof that the fat of the yellow-brown algal cells is a 
product of photosynthetic activity is the fact that when 
animals are placed in filtered water and so deprived of all 
food except that which reaches them from the algal cells and 
when the conditions for the nutrition of these cells are made 
as favourable as possible, e. g. by the addition of extra nitro- 
gen in such form as potassium nitrate, then so long as the 
animals are exposed to light their yellow-brown cells continue 
to contain oil globules. Thus, in one experiment, animals 
were placed, some in filtered sea-water in the dark, others in 
filtered sea-water with extra nitrogen in the light. After 
fourteen days (August 21—September 5), though there was 
no fat in the algal cells of those kept in the dark, fat-globules 
were still present in the yellow-brown cells of the light-kept 
animals. It is therefore to be concluded that the fat-globules 
of the algal cells of C. paradoxa are reserve products of the 
photosynthetic activity of these cells. 
It follows naturally from the foregoing experiments and 
conclusions. that the fatty reserves of the yellow-brown cells 
are drawn on to supply material for the growth and metabo- 
lism of these cells. ° But there is evidence that the reserves 
of fat in the algal cells are also drawn upon and utilised by 
the animal tissues. 
The general proof that the yellow-brown cells do pass on 
food substances to the animal tissues will be given later. That 
the reserve-fat of the algal cells is one of the substances 
transferred to the animal the following observations render 
probable : 
In the first place, the tissues of animals whose yellow- 
brown cells are rich in reserve-fat also contain large numbers 
of globules of similar nature. These fat-globules, lying in 
cells of the animal tissue, have the same optical properties 
as, and give reactions similar to, those of the algal cells. 
In the second place, the appearance of the fat and its relation 
to the yellow-brown cells is, in freshly captured animals, 
most suggestive of secretion, recalling almost the appearance 
