May, 1903 .] Galls and Insects Producing Them. 
427 
growth of cells allowing the leaflet to enlarge and form the larval 
chamber between the two halves. The cells are at first normal, 
but gradually lengthen in an axis at right angles to the mid-rib. 
This can be readily observed by comparing the section of the very 
young gall (Fig. 61, a, b) with the section of the mature gall 
(Part I, Fig. 22). 
In Cecidomyia verrucola O. S. (Figs. 62 and 63) the youngest 
showed a condition in which the mesophyll part of the leaf was 
reduced or entirely removed by the larva. The upper epidermis 
and palisade cells, the lower epidermis and cells next to it, form 
the upper and lower walls of the larval chamber while the inter- 
mediate mesophyll is removed. The inner layers of cells, i. e., 
the cells next to the larval chamber, now grow and divide very 
rapidly, gradually filling almost the entire cavity and reducing 
the size of the chamber (Part I, Fig. 24). At the same time the 
gall is increasing rapidly in size. 
5. GALLS OF THE CYNIPIDAE. 
Although a large amount of material was collected, only three 
species were sufficiently complete to enable a satisfactory stud)’. 
However, several mature galls of species not described in Part I 
of this series were examined, and all agreed with the statements 
made concerning the general structural character of this group 
of galls. 
Callirhytis papillatus O. S. (Fig. 64) was especially difficult to 
collect because of its very small size and close resemblance in 
external appearance to other small Cvnipidous galls. Examina- 
tion of young Cvnipidous forms, which I am reasonably certain 
belong to this species, show all the zones in contact (Fig. 64). 
As the gall develops the protective zones and parenchyma zones 
separate but remain connected by elongated parenchymatous cells 
(Part I, Fig. 30). 
Dryophanta palustria O. S. (Fig. 65, a, b) appears as the leaves 
unfold from the bud. The youngest galls collected were not over 
two millimeters in diameter but showed the four zones well devel- 
oped, with the second and third zones in contact, thus verifying 
the views expressed in Part I. The cells of the innermost, or 
nutritive, zone were large and very granular. Evidently this zone 
was almost completely reduced by the larva in the specimen from 
which Fig. 29 of Part I was drawn. In the next, or protective, 
zone the cell walls were very thick. In the parenchyma zone the 
innermost cells were small and numerous and the walls were thin, 
and in both cases the long axis of the cells were at right angles 
to the surface of the gall. As the gall grows older the intercellu- 
lar spaces may become prominent among the cells of the paren- 
chyma zone (Fig. 65, b). Careful examination of a large number 
of specimens gave conclusive proof that the separation occurs 
