48 STEUCTUEE OF THE LEPIDOPTEEA 



certain butterfly that usually appears in the first week in May. 

 Before finally naming the day, he has to consider what the weather 

 has been during the last few weeks, and if he finds that this has 

 been much warmer than the average for the corresponding periods 

 in the past, he selects a day in April, earlier or later according to 

 the difference between the present season and the average. 



If he does not pay due attention to such considerations, he will 

 sometimes find that all the insects netted are shabby and much 

 worn, even though, under average conditions, he would be catching 

 newly emerged and brilliant specimens. This, then, will explain 

 how it is that we so often see in entomologists' periodicals startling 

 accounts of ' early captures,' and of the appearance of certain insects 

 late in the season that ought not to have emerged till the following 

 summer. 



I will give just one illustration of these variations. The beautiful 

 Orange Tip Butterfly (Plate I, fig. 7) generally appears about the 

 middle of May in the southern counties. Farther north it is of 

 course a little later. In the north of England it has been taken in 

 June ; and in Scotland as late as July. On the other hand, I have 

 taken it in Gloucestershire as early as March, on a rather bleak 

 day with a cold east wind ; and, withal, irr a field on the slope of the 

 Cotswolds fully exposed to the unfavourable breeze; but it was 

 evident that, in this case, the butterfly had been enticed from 

 its winter quarters by the milder weather of the few previous 

 weeks. 



It may be as well, in passing, to observe that it is not only the 

 pupa that is influenced by temperature. The hatching of eggs may 

 be forced by high temperatures, or be retarded by exposure to cold ; 

 and in nature the period of incubation varies with the seasons. 

 The larvae, too, grow faster or more slowly, or pupate earlier or 

 later from similar causes. And so no very definite date or period 

 can be assigned to any one stage of any insect. 



Now let us return to one of the chrysalides that we have already 

 watched through the earlier stages of its existence, and follow it in 

 its future development. 



It is now, as we say, in its quiescent or dormant condition, but 

 we must not suppose that it is always in a profound sleep, nor can 

 we say that it is insensible to its surroundings. Touch it gently or 

 surprise it with a puff of air from your mouth, and it will begin to 

 wag its pointed tail, sometimes with such vigour as to send the 

 body rolling round and round in its box. Lay it on a bed of cocoa- 



