APPENDIX. 49 



'The egg- passes through all the developmental stages in the 

 ovary ; when these are completed the egg is laid, and a minute or 

 two afterwards the larva breaks through the egg-shell. In each 

 division of the ovary the eggs undergo development one at a time ; 

 it therefore follows that they are laid at considerable intervals, so 

 that a long life becomes necessary in order to ensure the develop- 

 ment of a sufficiently long series of eggs. Hence it comes about 

 that the females' live a full year. Among other species of Cliryso- 

 mela two generations succeed each other in a year, and the duration 

 of life in the individual varies from a few months to half a year.' 



VIII. HYMENOPTERA. 



Cynipidae. I have been unable to find any accurate accounts of 

 the duration of life in the images of saw-flies or ichneumons ; but 

 on the other hand I owe to the kindness of Dr. Adler, an excellent 

 observer of the Cynipidae, the precise accounts of that family which 

 are in my possession. I asked Dr. Adler the general question as to 

 whether there was any variation in the duration of life among the 

 Cynipidae corresponding to the conditions under which the deposi- 

 tion of eggs took place ; whether those species which lay many 

 eggs, or of which the oviposition is laborious and protracted, lived 

 longer than those species which lay relatively few eggs, or easily and 

 quickly find the suitable places in which to deposit them. 



Dr. Adler fully confirmed my suppositions and supported them 

 by the following statements : 



' The summer generation of Neuroterus (Spatheg aster) has the 

 shortest life of all Cynipidae. Whether captured or reared from the 

 galls I have only kept them alive on an average for three to four 

 days. In this generation the work of oviposition requires the 

 shortest time and the least expenditure of energy, for the eggs are 

 simply laid on the surface of a leaf. The number of eggs in the 

 ovary is also smaller than that of other species, averaging about 

 200. This form of Cynips can easily lay 100 eggs a day. 



' The summer generation of DryopJianta (Spathegaster Tasckenlergi, 

 verrucosiis, etc.) lives somewhat longer ; I have kept them in con- 

 finement for six to eight days. The oviposition requires a consider- 

 able expenditure of time and strength, for the ovipositor has to 

 pierce the rather tough mid-rib or vein of a leaf. The number of 

 eggs in the ovary averages 300 to 400. 



E 



