THE NUMERICAL ASPECT OF OAK GALLS. 21 



l)ud, it went on witliout interruption to another, and 

 was altogether eighty-seven hours busily employed in 

 laying its eggs. In two buds I counted 582 eggs " 

 (' Alternating Generations,' p. 72). 



So accurately are the ova placed either within, or 

 upon, the cambium layer, that failure in gall-prodnction 

 is rare. 



The operation of egg depositing is a delicate one and 

 it demands much care and time. 



When NeuToterus lenticidaris settles on a bud, the 

 long and slender terebra is inserted near the apex and 

 pushed l^etween the leaf-scales down to the base of the 

 bud; then it curves upwards, penetrating a part of the 

 bud axis, until it conies into contact with that part of 

 the embryo leaf which will be the under-surface when 

 expanded ; the gall of Spatliegaster baccarirni then 

 develops. N. Iseviu^cnlus, whose mode of oviposition is 

 similar, requires from fifteen to twenty minutes to 

 perform the same operation. But piercing the vege- 

 table tissues is only one part ; the egg with its long- 

 stalk has to be pushed along until it reaches the termi- 

 nation of the puncture. For each egg a separate 

 tube has to be made in the bud, because the egg-stalk 

 occupies too large an amount of space in the tul^e to 

 allow another egg to be pushed hj the side of it. 



Efficiency is aimed at by the Cynips, and she is 

 rewai'ded for her labours and care by a high percentage 

 of satisf actor}" results. 



How it is possible for the insect to determine the 

 exact spot for the egg to lie is beyond the scope of 

 the present consideration of the phenomenon, except 

 to mention that certain tactile hairlets, whose bases are 

 connected with nerves, are situated on the ovipositor, 

 which are also employed in the discrimination between 

 leaf-buds and flower-buds. 



In comparison with the size of the abdomen the 

 ovaries are very large, and many species of the Cynipidas 

 contain enormous numbers of ova. 



The ovaries of Gi/nips Kollari have been shown l)y 



