isiti.^ 23 



rhizolitha, and petrificata, Calncampa (botli), 77. croceago, S. duhitata, C. miata, 

 Alucita, and some Depre.isariw. It would be desirable to extend tlie lists both in 

 Hifmenoptera and Lepidoptera, and especially to ascertain whether there are any 

 exceptions to these apparent rules. If not absolutely, tliey are very broadly true. 

 As to other Orders I have made fewer observations, and have not noted that many 

 have been specially recorded. I believe no Tenthredo hibernates as an imago. As 

 to Ichneumons, I learn from Mr. Bignell that their habits are very various, and in 

 some species have that indeterminate character (or "fluidity") that I refer to as 

 common among Coleoptera. Not a few hibernate as imagines, but the date of fer- 

 tilization is not recorded ; the capture of hibernated males in the spring, or their 

 absence, would be strong, if not perfect, evidence as to this point. Among Coleoptera 

 many species pass the winter niore or less awake rather than hibernate. Many others, 

 as the HyJesinids, ought not to assume the perfect state till spring, but a large pro- 

 portion do so in autumn ; these individuals hibernate and pair in spring ; there is, 

 indeed, among beetles a great apparent fluidity of habit, with no very defined date 

 for any stage to the degree we are used to in Lepidoptera. 



When do those beetles pair whose habit is like that of many weevils, take 

 Antkonomns pomorum as a type, which emerges in June or July and do not oviposit 

 till the following April, or even May ? 



The common Coccinellce, Dryops femorata , and one or two others that truly hi- 

 bernate, pair in the spring ; records of many others must exist. 



To return, however, to the Hymenoptera and Lepidoptera, where we are on 

 more fully explored ground, what is the reason for so decided a difference of habit ? 



It would seem that there was an advantage in autumn fertilization to this 

 extent, that there is probably always an unfertilized residuum, which must be in 

 proportion to area. Say that one 9 pei' square mile represents, for a particular spe- 

 cies, a sparseness of distribution in which she fails to be found by the (J, and that 

 this number (more or less) always remains unfertilized, this represents a loss that 

 must be much larger proportionately in the spring, when periiaps half the individuals 

 of the species have succumbed to the perils of hibernation, it will, indeed, in that 

 case be twice as great a loss as it would have been in autumn ; but, in a specially 

 disastrous winter in which, say, nine-tenths of the species have perished, it will be 

 ten times the loss. The number that fails (o be fertilized being an absolute and not 

 a proportional number. 



It is also possible to suppose that in the case of autumn fertilization, only half 

 the number of individuals having to survive, suitable hibernacula will be more easily 

 found, being proportionally twice as abundant, though probably suitable places for 

 wintering in are always in large excess of any requirements. 



If these advantages of autumn fertilization have led the Hymenoptera to adopt 

 that system, why have the Lepidoptera taken the opposite course? I do not think 

 anything can be made of the weather being more suitable in spring. 



There is room for much doubt whether there is any actual effect produced by 

 any possible advantage in either case, and whether the difference is not existing in 

 the natural habit of the two Orders. In Aculeates there is possibly (there certainly 

 is in Apis melUfiva) a necessity for fertilization occurring within a brief period after 

 exclusion ; whilst, as seen in various ants and bees, the fertilized 9 it'^J 'i^^ many 



