GALLS CAUSED BY GALL-WASPS 25 



brood it may be greatly prolonged, the larva remaining 

 unchanged for several years. The larvae of Callirhytis 

 glandium, which galls acorns, may delay metamorphosis for 

 three years. Mr. Fitch collected some galls in 1878 in 

 which the larvae were still living in 1881. The pupa is 

 white and fleshy. 



The imagines (perfect insects) are sluggish and of un- 

 interesting habits. The sexes are much alike; there is 

 no marked difference in coloration ; the males are a little 

 shorter and have longer and thinner antennae. The sexual 

 and agamic females show many points of difference. The 

 agamic are usually larger, differently coloured, and the 

 ovipositor differs both in form and size. 



In some species the imagines Eire so much alike that the 

 only certain test of identification is the gall from which they 

 have emerged. 



It is now generally agreed that cynipidous galls arise 

 from the irritation of the meristematic tissue by the move- 

 ments of the larva. The egg alone does not give rise to 

 gall growth, for in some cases it is deposited weeks before 

 the gall begins to form. Cameron* concluded " (i) that 

 there is no evidence that the venom has anything to do 

 with the origin of the gall — on the other hand, there is 

 every reason to believe that its use is to close the wound ; 

 and (2) that as observation shows that the mechanical 

 irritation produced by the birth and growth of the larva is 

 the primary factor in gall genesis, we may fairly conclude 

 that the theory of mechanical irritation is more in con- 

 sonance with observed facts than the infection one." There 

 is no permanent opening in the galls of the Cynipidae; the 

 larvae are immersed in the substance of the gall, and pupate 

 in it ; the imagines bore their way out. 



The galls may be only slightly attached to the plant, or 



more or less embedded in the tissue. If there is only one cell 



within, the gall is styled "monothalamous " or " unilocular " ; 



when many cells are present it is termed " polythalamous " or 



• " British Phytophagous Hymenoptera," vol. iv,, pp. 23, 24. 



