648 JULIAN 8. HUXLEY 
spheroids in clean sea-water. This, however, is probably due 
simply to a greater susceptibility of Perophora to laboratory 
conditions, in the same way as one species may develop well 
after artificial insemination in the laboratory, while a closely- 
related species cannot be got beyond early segmentation 
stages. 
(c) Dedifferentiation with Resorption. 
(1) Stolon Resorption.—In systems with healthy 
young or moderate-sized zooids which were changed to fresh 
sea-water daily, the interesting fact soon came to light that so 
long as the full tone of the zooid was maintained and its siphons 
continued wide open, it did not decrease in size at all, but 
maintained itself at the expense of the stolon. This would 
also occur sometimes when the zooid was in the form of 
a partially-differentiated bud (e.g. fig. 4, ef). The bud 
remained of the same size and at the same stage of development 
for over seven days, while the stolon was almost completely 
resorbed. 
Later it was found that in other systems in which the zooid 
portion was represented by similar developing buds, these 
might not merely maintain themselves but actually develop 
further into perfect zooids at the expense of the stolon, 
e.g. fig. 2, where in the course of three days a very great change 
in the relation of zooid and stolon has taken place. 
Tt is thus clear that in certain circumstances the zooid may 
be physiologically dominant over the stolon, and may either 
develop or maintain itself at the latter’s expense. 
(2) Zooid Resorption.—In other cases, however, 
a change in the opposite direction takes place. In most 
systems, after the lapse of a few days without change of 
water (and in some even when the water is changed), the 
premonitory signs of dedifferentiation become visible: the 
siphons close, the general tone decreases, and the whole animal 
shrinks slightly. But the sequel is quite different. Instead 
of becoming more and more opaque, on account of the cells 
of the various organs and epithelia becoming cuboidal and so 
bringing about a marked decrease in the size of all the cavities 
