AAA, FREDERICK KEEBLE. 
acts in an acid medium, since, when under certain circum- 
stances to be described presently the yellow-brown cells 
undergo digestion in vacuoles, the space between the wall of 
the vacuole and the cell undergoing digestion is occupied by 
a faintly pink fluid. The solid food is taken in through a 
mouth which is not recognisable when closed, but which is 
seen during the act of ingestion to be capable of an enormous 
gape (cf. Bronn’s ‘ Tierreich,’ iv, 68—71). 
The solid gut which consists of parenchymatous tissue has 
no clearly defined outline ; but its shape may be traced roughly 
by the positions which solid bodies fed to the animals take 
up in it. A convenient substance for this purpose is uric 
acid, the crystals of which are recognised readily, and which, 
unlike many inert substances, does not seem to provoke 
excretion. Not only may large quantities of this substance 
be ingested, but the crystals remain for a very long time in 
the digestive vacuoles. By such means it can be seen that a 
shert broad gullet passing back from the mouth gives off two 
successive pairs of transverse processes, and then ends in a 
broad but gradually tapering mass of granular tissue, which 
reaches almost to the posterior end of the animal. The 
lateral processes are connected with prolongations which run 
one on either side of the body forward almost to the level of 
the statocyte and also a short distance backward. It is note- | 
worthy that the two broad and prominent transverse bands 
of dark refractive material (concrement granules), Bronn 
(loc. cit.), which are so characteristic of C. paradoxa (PI. 26, 
fies. 4 and 5), and which von Graff regards as being of the 
nature of nitrogenous excretory substance, lie over the two 
pairs of transverse processes which connect the gullet with 
the large laterally placed parts of the gut. 
Mention may be made here of several attempts to infect 
larval C. paradoxa, whose bodies were free from yellow- 
brown cells, with the green, flagellated infecting organism 
of C. roscoffensis. he flagellated cells were ingested by 
C. paradoxa and transferred to large vacuoles, where they 
remained intact for several days with their eye spot and 
