D0 JULIAN 8. HUXLEY 
zooids. Complete resorption of very young buds has, however, 
been noted. When dedifferentiation is rapid, and especially 
in larger zocids, the connexion between zooid and stolon may 
be severed, and a spheroidal mass left isolated in the old 
tissue. ‘This, of course, precludes further resorption. 
Two further pomts of interest should be mentioned. The 
first is that the tunic of the zooid undergoes considerable 
decrease in size, presumably by means of some form of resorp- 
tion. ‘This reduction, as shown in the figures, is usually 
irregular, but I have seen cases of reduction in buds where 
the test remained closely apposed and of firm outline. 
The second is that the stolon, especially during the late 
stages of the process, performs spontaneous movements of 
contraction, thereby causing a rudimentary and irregular 
form of circulation through the system. This may be called 
stolon-circulation. ‘The contraction is effected by the 
ectoderm cells becoming cuboidal in one place and later 
extending again to become flattened * pavement ’-epithelium 
(fig. 24). Corresponding with these circulatory movements 
back and forth, the now minute zooid could be seen now to 
contract, now to expand slightly, cells moving from it ito 
the stolon or vice versa. A similar contractibility of the 
ectoderm J have also observed in the stolon of Clavellina, 
and in the coenosare of Hydroids (Campanularia and Obelia). 
During the resorption of the zooid the stolon usually grows 
in length, at least during the earlier stages (figs. 5, 6a). Later 
on the stolon often remains constant in size, or decreases 
slightly. It then becomes more or less opaque, owing to the 
accumulation in it of cells from the zooid. Such packed opaque 
stolons, however, may send out transparent slender new 
srowths at one or both ends. Quite often the final length 
may be greater than the original length, and buds may even 
be formed. The process of resorption may take a considerable 
time. ‘The zooid in fig. 9 took seven days in all, four days to 
the cessation of the heart-beat and three days more until 
only a stalk was left, but in other specimens it was much 
more rapid. For convenience the process may be divided into 
