528 



HYMENOPTERA 



CHAP. 



Fig. 349. Rhodites rosae, female. 

 Cambridge. 



Cynipidae will not go through their gall-making operations except, 

 under natural conditions. Giraud ^ attempted to obtain oviposi- 



tion, on gathered twigs of oak, 

 from flies in confinement ; but, 

 although he experimented with 

 thousands of specimens, they on 

 no occasion laid their eggs in, 

 the fresh shoots placed at their 

 disposal, but discharged their 

 eggs in little heaps, without 

 attention to the twigs. The 

 same observer has also called 

 attention to the fact that after 

 being deposited in a bud the eggs 

 of certain species of Cynips will 

 remain dormant without produc- 

 ing, so far as can be seen, any effect on the tree for a period 

 of fully ten months, but when the bud begins to develop and 

 the egg hatches then the gall grows. 



The exact mode in which the egg is brought to the requisite 

 spot in the plant is still uncertain. The path traversed by the 

 ovipositor in the plant is sometimes of considerable length, and 

 far from straight ; in some cases before it actually pierces the 

 tissues, the organ is thrust between scales or through fissures, so 

 that the terebra, or boring part of the ovipositor, when it reaches 

 the minute seam of cambium, is variously curved and flexed. 

 Now as the canal in its interior is of extreme tenuity, and 

 frequently of great length, it must be a very difficult matter for 

 the Qgg to reach the tissue where it should develop. The eggs 

 of Cynipidae are very remarkable bodies ; they are very ductile, 

 and consist of a head, and of a stalk that in some cases is five or 

 six times as long as the head, and is itself somewhat enlarged at 

 the opposite end. Some other Hymenoptera have also stalked 

 eggs of a similar kind (Fig. 357, A, Qgg of Zeucospis). It has 

 been thought that this remarkable shape permits of the contents 

 of the egg being transferred for a time to the narrower parts, and 

 thus allows the broader portion of the egg to be temporarily 

 compressed, and the whole structure to be passed through a very 

 narrow canal or orifice. It is, however, very doubtful whether 

 1 Ann. Soc. ent. France (4), vi. 1866, p. 198. 



