Sycamore gall. 1 6 1 



to develop on the leaf. The first leaves of the pricked . 

 trees, which had been kept indoors, unfolded themselves 

 on May 15. I was able to ascertain at once the presence 

 of an abundant formation of galls. One bud alone developed 

 five leaves on which I counted 14, 9, 6, 4, and 2 galls 

 respectively. 



On four of the trees there were galls, and on two none. 

 They had however all been pricked alike, but those without 

 galls were almost a month behind the others in growth ; 

 I therefore inferred that the larvae, when they escaped 

 from the egg, were unable to find the tissues of the plant 

 in a condition suitable for their development, and con- 

 sequently perished. The galls thus obtained were those of 

 Bathyaspis aceris. 



2. Bathyaspis aceris, Forster. 



Gall. The gall is formed on the leaves of the sycamore, 

 exactly as the galls of Spathegaster baccarmn on the leaves 

 of the oak. As the egg is deposited in the centre of the 

 bud, on a leaf as yet undeveloped, the structure of the leaf 

 is always more or less altered by it. As a rule, this 

 alteration is limited, as far as can be seen, to the galls 

 growing through and through the leaf, but sometimes when 

 several galls are situated side by side the leaf is completely 

 crumpled up. It also occasionally happens that the gall 

 is developed on the petiole, which then undergoes an 

 irregular enlargement. The galls which are situated on 

 the leaves are regularly rounded ; 5 mm. in diameter ; 

 green or greenish yellow, tinted with red on the side 

 exposed to the sun ; the surface is very slightly hairy 

 or quite smooth ; the walls of the gall when mature are 

 thin, somewhat solid, and enclose the large larva. The fly 

 emerges at the beginning of July. 



Fly. Size 2-2-5 mm. ; brownish yellow, lighter than the 

 agamous generation. All the body is of the same colour, 

 except the apex of the abdomen, which is a little darker 

 above. Villosity apparent on the face and the sides of the 

 thorax; very feeble or entirely wanting elsewhere. The 



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