DEDIFFERENTIATION IN PEROPHORA 649 
in the organism, the zooid remains transparent. At the same 
time, however, it decreases in size. It is, in fact, being 
resorbed into the stolon. Appearances indicating the 
occurrence of this process are also found in nature, though 
not commonly. Successive stages of the process are shown in 
figs. 4, a—b, 5, 6, 9, 12, and isolated stages in figs. 7, 8, 10, 11, 
13-15. 
After a very short time the siphons disappear entirely, 
and a spheroidal mass of two-thirds or one-half the zooid’s 
original diameter is left. In this, the ovoid heart, very little 
diminished in size, can always be seen pulsating steadily. 
A steady diminution of size continues, the heart too decreasing 
absolutely, although becoming relatively larger. A certain 
degree of opacity may appear, but it is never striking. 
At a certain moment the pulsation of the heart slows down 
and ceases. Soon after this the heart becomes invisible 
altogether. ‘Traces of other orgens are visible. At first they 
are somewhat masked by the slight opacity caused by accumu- 
lation of blood-cells in the shrunken zooid, but later, as the 
zooid becomes smaller and smaller, they become increasingly 
clear. At about the stage when the heart disappears they are 
seen as two or three translucent rounded bodies, some colourless, 
some faintly yellowish. 
The shrinkage continues after the disappearance of the heart, 
and soon the zooid comes to appear as a minute knob, scarcely 
bigger than the stalk connecting it with the stolon. This stalk 
represents the stolon-connexion of the original zooid, and has 
itself decreased in size, although but slightly. At this stage 
a single clear refractive area, which I take to be the vestige 
of the stomach, is usually the only structure to be seen in the 
knob. Finally the knob all but disappears, and a mere trace 
of the clear area remains visible. Presumably the stalk itself 
would also eventually become resorbed into the stolon, but 
resorption is much retarded after the cessation of the heart’s 
action, and becomes progressively slower and slower as the 
size of the zooid decreases, so that J have never actually 
observed this ultimate step in the resorption of fully-formed 
