266 STATES OF INSECTS. (Pupa.) 
closed from the pupa in the cold and stormy months of 
February and March, almost every day of which in cer- 
tain years is so ungenial that few insects could then sur- 
vive exposure, much less deposit their eggs and ensure 
the succession of a progeny. Now, were all these to 
make their appearance in the perfect state in the same 
year, it might happen that the whole race in a particular 
district would be destroyed. But this possibility is effec- 
tually guarded against by the beautiful provision under 
consideration, it being very improbable that three suc- 
cessive seasons should be throughout 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 pupz though disclosed in the summer are governed 
by the same rule, the prevention of the extinction of the 
species, by any extraordinary increase in a particular 
year of their natural enemies, seems the object in view *. ~ 
But though the intention be thus obvious, the means by 
which it is effected are impenetrably concealed. What 
physiologist would not be puzzled 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 observed by Mr. Jones with 
respect to the pupze of S. mendica. Reaumur found that 
when the skin of pupze was varnished, so as to prevent 
absorption, the appearance of the fly happened nearly 
two months later than in ordinary circumstances. Are 
we to conjecture that those of the moth just mentioned, 
or of E. lanestris, that are latest matured, from a greater 
2 Mr. Marsham makes a similar observation in Linn. T’rans., ubi 
supr. 
Se 
ee a ee 
