646 JULIAN 8. HUXLEY 
However, Driesch also mentions in one of his papers (1906) 
that he had been able to secure dedifferentiation in whole 
individuals. In my work I used whole individuals only. With 
them I found that the simplest method of obtaining dedifferen- 
tiation was to leave unchanged the water in which the organisms 
were kept, the accumulation of toxic waste products probably 
initiating the process. It was also found that only young 
individuals underwent dedifferentiation easily, mature and_ 
half-grown zooids speedily dying. 
When full dedifferentiation, whether of half or whole zooids, 
occurs in Clavellina, a spheroidal white mass results, in which 
all the organs are very much simplified, both morphologically 
and histologically, becoming reduced to a series of separate 
sacs, some simple, others compound, of roughly spherical 
shape with walls of embryonic-looking cuboidal cells. On 
being replaced in clean water the opaque mass usually grows 
out to form a new perfect zooid, quite normal but smaller than 
the original; and this alternation of differentiation and 
dedifferentiation may be repeated several times. It is obvious 
that the term dedifferentiation may be applied equally to all 
retrogressive changes resulting in simplification of visible 
structure, provided that the reduced tissues remain alive, 
whether or no redifferentiation from the reduced condition 
is possible or not. When it is possible, an added interest 
attaches to the whole phenomenon; but dedifferentiation is 
essentially similar whether subsequent redifferentiation can 
occur or not, just as differentiation is essentially similar in 
all cases whether subsequent dedifferentiation can occur 
or not. 
In Perophora similar methods were at first adopted, the 
animals being kept in watch-glasses contaiing approximately 
either 5 or 7-5 c.c. of water. 
Zooids that were adult or more than half-grown never 
achieved successful reduction. They all died after a few days, 
but always after a preliminary attempt at dedifferentiation. 
The siphons were closed, all appearance of vigour and tone was 
lost, the body became contracted and opaque. The appearance 
