CODIUM. 339 
distinctly separated from the outer at the base, leaving a 
small chamber between the plug-like septum and itself 
(compare fig. 20, P]. III.). Similarly, at the apex of the 
sporangium, a like chamber is formed, and the inner wall 
itself, as shown in fig. 16, swells and exhibits very definite 
lamellation. The occurrence of these cavities at the base 
and apex of the sporangium was obviously noted both by 
Derbes and Solier and by Harvey, for their figures of the 
sporangium illustrate, though somewhat roughly, the 
peculiarity to which we draw attention. The sporangial 
cavity is from half to three quarters full of a dark green 
mass which, on careful focussing, is seen to be composed 
of spherical bodies, each crammed with chloroplasts. 
Notwithstanding the fact that we examined hundreds 
of sporangia for long periods, and extending over three 
months, only once were we so fortunate as to see the zoo- 
spores escape. As described by Derbes and Solier, they 
escaped en masse, the apex of the sporangium rupturing 
suddenly, probably owing to pressure exerted from within 
by the swollen inner layer of the sporangium wall. The 
ereen mass gradually dissolved in the sea-water (in which, 
of course, the observations were made), and individual zoo- 
spores freed themselves and swam off. ‘The zoospores were 
dark green, with a clear apex, and showed, in the apical 
region, a body which was doubtless the nucleus described 
by Berthold. Each was provided with two cilia. We 
were unable to keep the zoospores alive until germination 
had ensued, though we purpose repeating our observa- 
tions in the hope of solving the question as to whether 
they are zoospores or gametes, as Berthold believes. 
The sporangium is, early in its development, isolated 
from the palisade cell by an annular thickening in its 
narrow pedicel (PI. IIL., fig. 20). This thickening becomes 
finally a complete plug, and after the contents of the 
