YELLOW-BROWN CELLS OF CONVOLUTA PARADOXA. 461 
to develop when removed from the body. ‘There can be 
little doubt that this failure on the part of the green cells of 
C. roscoffensis to maintain themselves when separated 
from the animal is due to the fact that they undergo whilst 
in the animal body partial nuclear degeneration. The same 
is probably true of the yellow-brown algal cells of C. para- 
doxa. It being impossible to isolate viable yellow-brown 
cells from the animal the only alternative is to seek among 
the weed for a corresponding form, to cultivate it, and apply 
the infection test. Though yellow-brown cells, resembling 
in the most striking way those of the animal, are to be met 
with occasionally, especially in the capsule flora (Plate 28, 
fig. 17), and though in one instance a brown cell with elon- 
gated anterior end very suggestive of a flagellated organism 
was observed on an egg-capsule (Plate 28, fig. 16), the 
isolation of the free alga which, when in the animal, gives 
rise to the yellow-brown cell, has not yet been accomplished. 
The earliest stage yet observed shows the body of the 
animal to contain a single algal cell (Plate 28, figs. 10—15). 
The size of this cell varies considerably in the different 
cases in which it has been seen. In one example the cell 
was spherical, 7-4 in size, with greenish-yellow chloro- 
plasts. In another it was of oval shape, measured 16:5 p, 
and exhibited, like the yellow-brown cells of fully infected 
animals, but in a more marked manner, a peripheral series of 
flattened yellow chloroplasts with a number of pale grey- 
yellow chloroplasts occupying the body of the cell. In yet 
other cases, in which more than one cell was present, the 
infecting alga exhibited a large, clear, transparent region, a 
- group of flattened brown chloroplasts pointed at either end 
pressed against the wall of the cell, and a number (8—16) of 
pale yellow structures more like daughter-cells than mere 
chloroplasts. ‘his appearance was strikingly exhibited in 
one case, where the animal contained five algal cells, of 
which the largest was 37 x 37 pu, the others 16—18 pn. 
The large cell was surrounded by transparent thickish wall, 
against one side of which the elongated, dark brown chloro- 
