OF PAPILIONACEOUS INSECTS. 53 
greatest cold; which can be ascertained by squeezing 
them with the nail of the finger. ‘This may arise 
from their constituent parts being oleaginous or 
spirituous, or from some inherent psinciple adapted 
to resist the power of cold.” 
We are not at all enlightened by what Spallanzani 
has offered as a cause why eggs are enabled to re- 
sist the effects of cold, as he has given us no satisfac- 
tory explanation of the phenomenon. 
He proceeds, “ If eggs do not freeze, it is probable 
that the included embryoes do not freeze. Is there 
anything surprising, therefore, that they are capable 
of resisting that cold which proves fatal to their 
contained insect when produced? Perhaps, for the 
same reason, (and I can perceive no applicable 
objection, ) animalecula concentrated, or in the germ, 
can support a degree of cold which they are incap- 
able of enduring when emerged. 
«Tt may be asked, as the temperature of freezing 
still retains a portion of heat, why should it not 
develop the germs of the most minute animaleula ? 
If we had never seen any eggs hatched but those of 
birds, which require a hundred and four degrees, 
we should have naturally concluded that all others 
required the same. A slight knowledge of the 
physiology of minute animals, instructs how many 
kinds produce at a much lower temperature. The 
eggs of butterflies and many other insects hatch at a 
temperature so low as forty-five degrees. If these 
