1921] WELLS—ZOOCECIDIA 361 
vary from the simplest type in which there is but a slight inhibition 
of differentiation, to the advanced condition in which differentia- 
tion is practically inhibited, only a mass of homogeneous tissue 
resulting. In the prosoplasmas the contribution of the plant is 
practically confined to the furnishing of cell types merely, and not 
differentiation and tissue form conditions. 
2. THE ADULT, CECIDOzOON (ImAGO).—(a) Siructural aspects.— 
In the lowest cecidozoons, Rotifera, Copepoda, Nematoda, and 
Acarina, the adult stages as well as the larval stages are concerned 
in gall-making. With some unimportant exceptions in the Acarina 
galls, the cecidia are all kataplasmas. Above these groups we 
have but one genus in which the adult is concerned in definite gall 
formation, the genus Pontania of the Tenthredinidae (saw flies). 
The terebra’s mechanical injury plus the introduction of a specific 
liquid substance results in a kataplasma of an advanced type, for 
the lack of differentiated tissues is a striking characteristic of 
these galls. The prevailing condition among insect cecidozoons, 
however, is that in which the larval stages only are concerned in 
gallformation. This is invariably true if the galls are prosoplasmas. 
(b) Behavior aspects —Throughout all gall-making groups the 
instinctive behavior of the adults is a factor with regard to resultant 
gall conditions. Choice of plant part attacked, number of eggs laid 
at one point, time of attack, all have something to do with resultant 
characters. From the standpoint of the fundamental nature and 
specificity of the individual gall, however, these behavior aspects 
play but a very minor réle. 
. THE LARVAL CEcID0ozoon.—In the larval cecidozoon and its 
eraliitions we find par excellence the creators of phylogenetic lines, 
for all prosoplasmas, as heretofore indicated, are the result of 
larval and not adult activity. Another generalization is the fact 
that prosoplasmas are practically confined to the Insecta; only a 
few low prosoplasmas of the Acarina are an exception, 
Phylogenies of zoocecidia 
Before presenting the outlines of the phylogeny in the various 
groups it will be desirable to point out some fundamental relation- 
ships between the kataplasmas and the prosoplasmas. KistTEr, 
