_Cynipidae._ I have been unable to find any accurate accounts of the duration of life in the imagos 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 deposition 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_ (_Spathegaster_) 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 _Dryophanta_ (_Spathegaster Taschenbergi_, _verrucosus_, etc.) lives somewhat longer; I have kept them in confinement for six to eight days. The oviposition requires a considerable 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. ‘The summer generation of _Andricus_, which belongs to the extensive genus _Aphilotrix_, have also a long life. I have kept the smaller _Andricus_ (such as _A. nudus_, _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 _Dryophanta_ and _Biorhiza_ even longer. I have kept _Dryophanta scutellaris_ alive for three months. The number of eggs in these agamic _Cynipidae_ is much larger: _Dryophanta_ and _Aphilotrix_ contain 1200 and _Neuroterus_ about 1000.’