YELLOW-BROWN CELLS OF CONVOLUTA PARADOXA. 447 
chloroplasts are somewhat affected by the presence of the 
cell in the animal tissue, and, shrunken somewhat, appear 
darker in colour (Pl. 27, fig. 8, and Pl. 28, figs. 11, 12, and 
13), or it may be that the differences indicate a real 
dimorphism of the chloroplasts. 
The wall of the yellow-brown cell is extremely delicate, 
and gives no staining reaction whereby its nature may be 
determined. It is not composed of cellulose. A central, 
spherical nucleus staining green with methyl-green acetic 
may be demonstrated in many of the cells. Where present it 
lies about the middle of the cell in a sheath of protoplasm from 
which radiating strands run toward the periphery (Pl. 28, 
fig. 18). In some preparations the nucleus, slung in the 
manner just described, appears to le at the base of a colour- 
less “neck” of protoplasm in the same position as that in 
which it occurs in a chlamydomonas cell. Occasionally two 
nuclei may be seen in a yellow-brown cell, at other times the 
cell appears to have divided, but division of the nucleus not 
to have taken place so that a nucleus occurs in one part, and 
not in the other (Pl. 28, fig. 18 d). 
(b) The Photosynthetic Activity of the Yellow- 
brown Cells.—The structure of the yellow-brown cells of 
C. paradoxa points to the conclusion that these bodies are 
of the nature of alge. Other evidence based on their origin 
and given in Section III confirms this conclusion. 
Now if the yellow-brown cells are of the nature of algz, and 
if, as shown, they divide and grow in the animal tissue, it is to 
be expected that they may exhibit photosynthetic activity. 
Unfortunately but little is known either of the nature of the 
-substances photosynthesised by members of the different 
groups of the brown and yellow-brown algz or of the form in 
which these substances are stored as reserves in the plant-cells. 
According to Hansteen (1900) the reserve-substance 
formed from the product of photosynthesis in the Pheo- 
phycez (brown alge) consists of refractive globules of a 
carbohydrate which he calls fucosan. Crato (1893) holds 
that the reserve-substance of the brown alge is contained 
VOL. 52, PART 4.—NEW SERIES. 35 
