50 THE DURATION OF LIFE. 



' The summer generation ofAndricus, which belongs to the exten- 

 sive genus AphilotnX) have also a long life. I have kept the smaller 

 Andricus (such as A. nudiis, A. cirratus, A. noduli) alive for a week, 

 and the larger (A. inflator, A. curvator, A. ramuli) for two weeks. 

 The smaller species pierce the young buds when quite soft, but the 

 larger ones bore through the fully grown buds protected by tough 

 scales. The ovary of the former contains 400 to 500 eggs, that of 

 the latter over 600. 



'The agamic winter generations live much longer. The species of 

 Neuroterus have the shortest life ; they live for two weeks at the 

 outside ; on the other hand, species of Aphilotrix live quite four 

 weeks, and Dryopkanta and BiorMza even longer. I have kept 

 DryopJianta scutellaris alive for three months. The number of eggs 

 in these agamic Cynipidae is much larger : Dryoplianla and Aphilotrix 

 contain 1200 and Neuroterus about 1000.' 



It is evidently, therefore, a general rule that the duration of life 

 is directly proportional to the number of eggs and to the time and 

 energy expended in oviposition. It must of course be understood 

 that, here as in all other instances, these are not the only factors 

 which determine the duration of life, but many other factors, at 

 present unknown, may be in combination with them and assist in 

 producing the result For example, it is very probable that the 

 time of year at which the images appear exerts some indirect 

 influence. The long-lived Biorhiza emerges from the gall in the 

 middle of winter, and at once begins to deposit eggs in the oak 

 buds. Although the insect is not sensitive to low temperature, for 

 I have myself seen oviposition proceeding when the thermometer 

 stood at 5 R., yet very severe frost would certainly lead to inter- 

 ruption and would cause the insect to shelter itself among dead 

 leaves on the ground. Such interruptions may be of long duration 

 and frequently repeated, so that the remarkably long life of this 

 species may perhaps be looked upon as an adaptation to its winter 

 life. 



Ants. Lasius Jlavus lays its eggs in the autumn, and the young 

 larvae pass the winter in the nest. The males and females leave 

 the cocoons in June, and pair during July and August. The males 

 fly out of the nest with the females, but they do not return to it ; 

 ' they die shortly after pairing.' It is also believed that the females 

 do not return to the nest, but found new colonies ; this point is 



