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 

 3'oung 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 entire!}^ 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, onl}- three 

 species were sufficiently complete to enable a satisfactory study. 

 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 papillafus O. S. (Fig. 64) w^as especially difficult to 

 collect because of its ver}- small size and close resemblance in 

 external appearance to other small Cynipidous galls. Examina- 

 tion of young Cj-nipidous 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 b}- elongated parenchymatous cells 

 (Parti, Fig. 30). 



Dryophaiita palustria O. S. (Fig. 65, a, b) appears as the leaves 

 unfold from the bud. The 3'oungest 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 Vi\z.y become prominent among the cells of the paren- 

 ch3'ma zone ( Fig. 65, b). Careful examination of a large number 

 of specimens gave conclusive proof that the separation occurs 



