1921] WELLS—ZOOCECIDIA 371 
is from the beginning in contact with meristem, no such regression 
is possible or necessary. This situation will be developed at 
greater length in the general discussion. 
Within the prosoplasmas themselves innumerable examples of 
recapitulation may be pointed out, two of which may be men- 
tioned. In the ontogeny of the cecidium Amphibolips ‘inanis, the 
gall passes through the spongy stage illustrated by Amphibolips 
confluentus before it reaches the mature condition with radiating 
fibers. In the ontogeny of Oligotrophus annulipes (European) a 
juvenile stage is passed through which is almost exactly repro- 
duced in an adult gall (Cecidomyia sp.) on the same host. Hovarp 
(7), in reporting the resemblance of these two stages, fails to 
suggest the evident recapitulation interpretation. 
Discussion 
The foregoing part of this paper presents the results gained in 
the application of certain fundamental conceptions regarding 
cecidia which are concerned with the evolution of these structures. 
These conceptions have their historical background, as already 
indicated, but it will be well to review them in the light of modern 
genetic and phylogenetic theories, and point out their synthesis 
which, with the application of them in constructing the phylo- 
genetic trees, constitutes the chief contribution of the present 
paper. 
Before entering upon this constructive work, however, it will 
be necessary to clear the ground of certain false conceptions which 
have held sway to the present time, such as the interpretation of 
Kuster, Cosens, and others, who hold that all gall charac- 
ters are but the expression of active or latent normal host plant 
characters. CosENs and SINCLAIR (4) state that there remains no 
authentic instance of any organ or tissue in a gall that is new, 
ontogenetically or phylogenetically. This interpretation is clearly 
fallacious, for it is the essential newness of prosoplasmas which 
constitutes their most important characteristic. This newness 
appears perhaps in its most striking manner in the form charac- 
ters of the tissues, which implies of course the form of the gall 
as a whole. Since form characters are of utmost importance 
