DEDIFFERENTIATION IN PEROPHORA 655 
lower grades of strength adversely affect the zooid, but only 
affect the stolon sufficiently to inhibit its growth, not to cause 
its dedifferentiation. Partial resorption may take place in 
these circumstances. 
Still lower concentrations have no appreciable effect upon the 
stolou, but yet advergely influence the more sensitive zooid. 
The stolon is thus able not only to maintain its form, but to 
grow. The zooid starts dedifferentiation, and this is followed 
by resorption, which, typically, is complete. Finally, we get 
dilutions beyond which no effect is produced on the zooid or 
the stolon, with the result that the normal dominance of the 
zooid is maintained, and it is the stolon which is resorbed. 
We thus see that these processes occurring in nature can 
be experimentally controlled to a considerable degree. Other 
toxic agencies were not tried on Perophora; but from what 
we know of the reactions of other organisms we should expect 
that the results of KCN treatment are non-specific, and that 
essentially the same phenomena would occur in other toxic 
solutions. 
Our results of observation are therefore to be thought of as 
due to the following causes : 
(1) In Perophora, in the absence of food, there is a competi- 
tion for nutriment among the parts of the colony. 
(2) In normal conditions, in the absence of food, the most 
active and differentiated parts (the zooids) are dominant. in 
this competition over the less active and differentiated parts 
(the stolons), which are used up as nutriment by the zooids. 
(3) Correlated with this difference of success in competition 
there is a difference of susceptibility, the more highly-organized 
zooids being more susceptible than the stolon to unfavourable 
agencies. 
(4) he result of unfavourable agencies on Perophora is to 
cause dedifferentiation. 
(5) Once dedifferentiation has started the zooid ceases to be 
more active than the stolon, and so ceases to be dominant 
in the intra-organismal struggle. 
(6) In Perophora dedifferentiation may be followed by 
aoe 
