1921] WELLS—ZOOCECIDIA. 367 
sclerenchyma layers around the larval chambers. If the apical 
meristem is used as a basis of operation, we get such a primitive 
gall as shown in (21), and, either through a burying process on 
the part of the larva or through the up-walling mode of overgrowth, 
we pass through such a stage as (22).to the prosoplasmatic condition 
of (23), ending in such a highly specialized type as shown in (24). 
CHALCIDAE (Hymenoptera) (pl. XXII).—This family is repre- 
sented very insignificantly by a few genera producing simple corti- 
cal enlargements (r). ) 
TEN AE (Hymenoptera) (pl. XXII).—A few genera of 
gall makers represent this family. Some species form simple, 
cortical stem hyperplasias (1); others a rather well defined leaf 
gall with such homogeneous tissue within it that it may be regarded 
as but a high kataplasma (2). One European form produces a very 
low kataplasma in inducing an enrolled condition of the leaf (3). 
The second form is of especial interest because its initial stages are 
known to be induced through the action of a chemical stimulus 
emitted by the adult female at the time of egg-laying. 
CyNIPIDAE (Hymenoptera) (pl. XXII) —Thisfamily is recognized 
by all students to be the most remarkable from the standpoint of 
variety and complexity of the galls produced. This is true even 
though the largest number of these galls is found on one host 
genus (Quercus). The vast majority of cynipid galls are proso- 
plasmas. Four independent points of ‘origin are presented, 
though three of these may conceivably have been derived from 
the primitive leaf kataplasma (10), as indicated by the arrow lines. 
In the evolution of the stem galls we find a progressive series 
(1-4) related to the orientation of the larva within the stem. 
This situation is related primarily to the placing of the egg by the 
Ovipositor of the adult females, for so far as known these larvae 
are not migratory. Any of the stem kataplasmas shown may 
become elementary prosoplasmas through the differentiation of a 
sclerenchyma layer around the larval chambers, a parenchymatous 
nutritive layer being left as a lining. In the diagram only the 
medullary (4) and cortical (5) types of prosoplasmas are shown. 
From the latter has been evolved the interesting dehiscence form 
shown in (6). beats 
