Insects. 4951 



morlales, plus caeperunt sapere." But how are we to begin to be wise, if the ex- 

 perience of practical men is bottled up, and explodes with indignation when some one 

 less fortunate expresses an opinion that the only recorded doctrine is the correct one ; 

 and ibis question of hybernation is, I confess, to me one of great interest. At the 

 risk of being thought obstinate, I must still express my opinion that the scheme of 

 insect-life, so far as we understand it, is the death of the imago before winter — as soon, 

 in fact, as the object of its existence is attained, viz. the procreation of its species ; 

 and the extent to which the pupa will bear cold, in comparison with the imago, has 

 been a fruitful and interesting subject of comment in the 'Zoologist; and I think 

 that, where the opposite fact is shown to exist, viz. when the imago can bear the cold, 

 and the pupa, according to your experiments, cannot, this may be considered a 

 casual and not a constant feature in insect-life. Mr. Doubleday, however, in a private 

 note, dissents from this view, and, as I think his opinion at all times valuable, and 

 especially so on practical points connected with the Lepidoptera, and, as I am sure 

 any additional facts will be as interesting to your readers as they have been to me, I 

 will quote (with his permission) a part of his letter. I will premise that the first part 

 of the extract refers to an objection I took to his definition of a double brood in the 

 1 Zoologist' for September (Zool. 481 1) : I suggested that every escape from the pupa 

 in the same year ought to be considered a brood, otherwise the cycle of single-brooded 

 insects being only completed in the two halves of separate years, the case would not be 

 included in his definition. The following is the extract: — " I quite agree with you 

 about double broods, and your definition is better than what I wrote in haste, though, 

 at the same time, mine is correct. The changes are gone through in twelve months by 

 each brood; for instance, the eggs of G. Illunaria are deposited in April — these hatch 

 and produce moths in July, from which brood larvae are hatched which become pupae 

 in the autumn, and produce moths the following March. The eggs of G. Rhamni, laid 

 at the same time, produce larva? which become butterflies in August, which live on till 

 the following April, and then deposit their eggs: of course there is only one brood in 

 the twelve months. Rumia Crataegaria differs from any other British species, as far 

 as I am aware, in its broods : it emerges from the pupa state at three different periods 

 of the same year, viz. April, June and August ; but the June brood is not the produce 

 of the April moths, but of those of the preceding August, which pass the winter in the 

 larva state and feed again in the spring, while those from the June brood become 

 pupa in the autumn and produce the moths in April: the specimens which appear in 

 June are always larger and finer in colour and markings than those of the other two 

 broods. I cannot at all agree with you that the hybernation of the perfect insect can 

 be called a casual occurrence: an event can only be casual which is out of the regular 

 course of nature, which the hybernation of certain species is not. You say, but ' I still 

 consider that the general scheme of insect-life is the death of the imago after the 

 object of its existence is attained, viz., that of procreating its species.' I admit that 

 this is correct; but many species never seem to have any sexual desire till after hyber- 

 nation, and therefore without it the end of their existence would not be attained. 

 I believe species which hybernate never copulate in the autumn (I am speaking of 

 Lepidoptera). Out of the thousands of Glaea Vaccinii, Spadicea and Satellitia that 

 I have seen at sugar in the autumn I never saw any attempt at sexual intercourse ; 

 but when they re-appear in the spring I have seen scores of pairs in cop. on the trees. 

 I never saw Vanessa Io, V. Atalanta, or the last brood of Urticae copulate in autumn : 

 the males take no notice whatever of the females ; but in the spring it is not uncommon 



