STATES OF INSECTS. (Pupa.) 265 
acute lepidopterist, in one of his excursions captured a 
female of Spzlosoma mendica, another moth, which laid a 
number of eggs, thirty-six of which produced caterpil- 
lars : all these fed, spun their cocoons, and went into the 
pupa state in the usual manner, but at the proper season 
only twelve produced the fly. As this was no uncommon 
circumstance, he concluded that the rest were dead: to 
his great atsonishment, however, in the next season 
twelve more made their appearance ; and the following 
year the remainder burst into life, equally perfect with 
the foregoing *. In this extraordinary result, which also 
occasionally has been observed to take place in the em- 
peror-moth (Saturnia Spinz), the privet-hawkmoth (Sphinx 
Ligustri), and that of the spurge (Dezlephila Euphorbia)”, 
and other species,—it is clear that something besides 
mere size and temperature is concerned : for, these cir- 
cumstances being precisely alike, one pupa arrives at 
maturity in six months, and another of the same brood 
requires between two and three years. We can guess, 
that the end which the All-wise Creator has in view, in 
causing this remarkable difference, is the prevention of 
all possibility of the destruction of the species. rio- 
gaster lanestris and Spilosoma mendica, &c., for instance, 
are doomed, for some reason unknown to us °, to be dis- 
* Marsham in Linn. Trans. x. 402. 
® Meinecken found, that of several pupa of Saturnia Spini, 
some kept all winter in a room heated daily by a stove, and others 
im a cold chamber, some of both parcels appeared in March (none 
earlier), and some of both had not appeared in July, though evidently 
healthy. Naturf: viii. 143. 
¢ 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. 
