652 JULIAN S. HUXLEY 
actual migration of single cells out of their union in the tissues 
into the cavities of the body (in Hydroids into the coelenteron, 
in Stenostomum into the parenchyma, in Perophora into the 
haemocoel). In no other way can we explain the rapid decrease 
in size of the zooid, or the marked increase in the number of 
cells in the cavities. The stolon in Perophora always becomes 
crowded with cells during the later stages of resorption. I have 
seen no sign of the cells disintegrating on release, there being 
no increase in the number of granules, &c., in the plasma ; 
and the process can certainly not be explained as due to the 
using up of cells as nutriment in situ. 
We have thus the singular spectacle of the organs and 
tissues unbuilding themselves. It is as if a house were to 
become smaller and smaller through individual bricks leaving 
their places here and there in the walls and accumulating in 
the passages and garden, the rooms meanwhile closing the gaps 
in their walls and progressively diminishing in size. 
During the process it appears that dedifferentiation also is 
going on. For one thing, the ectodermic epithelium becomes 
more and more cuboidal, and then also all cells that appear 
in the blood-stream are of a simple, irregularly-rounded type, 
and not visibly specialized in any way. 
The long persistence of the heart as a functional organ, and 
its final sudden disappearance are closely paralleled in simple 
dedifferentiation in Clavellina. 
Presumably what occurs when the stolon is resorbed into the 
zooid is similar, the cells of the ectodermic epithelium and of 
the endodermic partition also becoming dedifferentiated and 
migrating out of the tissues into the blood-stream. The 
process is merely not so remarkable here, owmg to the less 
differentiation of the tissues involved, and the subordinate 
status of the stolon as an organ. ‘To sum up, we find that in 
Perophora (and in Campanularia) adverse conditions lead to 
a form of reduction in which dedifferentiated cells migrate 
out of their fixed position in the tissues into the general cavity 
of the body, and the whole differentiated zooid finally dis- 
appears by resorption. This combination of deditterentiation 
