THE CYNIPID.E AFFECTING THK OAK. 29 



is concealed within the abdomen. The seta is a very 

 stiff bristle nnited to the interior of the abdomen and 

 controlled by five distinct sets of muscles. If a 

 transverse section of the terebra be examined it will 

 be seen that the seta occupies about half the area, 

 which is circular. The spiculge are alike in outline 

 and serration, and occupy the remainder of the area. 



The action of the ovipositor when making a hole for 

 the insertion of an egg is very similar to the move- 

 ments of the puncturing or stinging apparatus of other 

 aculeate Hymenoptera; e. g. wasps and bees. 



So deeply and firmly do the organs penetrate the 

 plant tissues that the insect is sometimes unalile to 

 withdraw them, and they are either broken off or torn 

 away from the abdomen together with the mechanism 

 which controls them. 



Some of the oak gall Cynipidie require from fifteen 

 to twenty minutes to deposit one egg (e. g. Neuroterus 

 Ixviitscnlus). 



The actual process of oviposition can be divided into 

 three stages, which, according to Adler (' Alternating 

 Generations,' p. 119), are these : " (1) The canal is 

 bored, tlie ovipositor gliding under the imbricated scales 

 to the base of the bud, and then being driven into the 

 centre of the bud-axis. (2) The egg passes out of the 

 ovarium to the base of the ovipositor, where the egg- 

 stalk is pinched between the two spiculge, and the egg 

 is pushed along the ovipositor. (8) After the point of 

 the ovipositor is withdrawn the egg-body enters the 

 pierced canal and is pushed forward by the ovipositor 

 until it reaches the bottom." 



The number of eggs deposited by a single individual 

 varies. Those of the summer generations produce from 

 200 to 400 eggs, the agamous generations several 

 hundreds more. 



The eggs of this family are remarkable in having 

 what is known as an egg-stalk which is attached to the 

 anterior part of the egg. It is a continuation of the 

 yolk sac, and has the function of a respiratory organ 



