STATES OF INSECTS. 267 



son unknown to us a , to be disclosed from the pupa in 

 the cold and stormy months of February and March, 

 almost every day of which in certain years is so ungenial 

 that few insects could then survive exposure, much less 

 deposit their eggs and ensure the succession of a progeny. 

 Now, were all these to make their appearance in the per- 

 fect state in the same year, it might happen that the 

 whole race in a particular district would be destroyed. 

 But this possibility is effectually guarded against by the 

 beautiful provision under consideration, it being very im- 

 probable that three successive seasons should be through- 

 out unfavourable ; and without such occurrence, it is clear 

 that some of the race of this moth will be preserved. In 

 the case of other moths, whose pupae though disclosed in 

 the summer are governed by the same rule, the prevention 

 of the extinction of the species, by any extraordinary in- 

 crease in a particular year of their natural enemies, seems 

 the object in view b . But though the intention be thus 

 obvious, the means by which it is effected are impene- 

 trably concealed. What physiologist would not be puz- 

 zled with the eggs of a bird, of which one-third should 

 require for their hatching to be sat upon only a fortnight, 

 another third a month, and the remainder six weeks? Yet 

 this would be an anomaly exactly analogous to that ob- 

 served by Mr. Jones with respect to the pupae of A. men- 

 dica. Reaumur found that when the skin of pupae was 

 varnished, so as to prevent absorption, the appearance of 



a The exclusion of certain moths, &c. from the pupa is probably 

 regulated by the time their eggs require to be hatched, and the ap- 

 pearance of the leaves that constitute their appropriate food. 



b Mr. Marsham makes a similar observation in Linn. Trans., ubi 

 snpr. 



