11 
others, which are deposited on twigs or bark, may.be 
found protected by a peculiar cement-like coating, or by 
down from the parent insect, or, in the case of the 
common Apple Scale, by the dead body of the female. 
We know, from the often-quoted experiments of 
Spallanzani, that insect-eggs have been found to bear a 
four hours’ exposure to a cold of 38° below zero of 
Fahrenheit without any apparent loss of vitality ; and 
John Hunter found that, although eggs that be exposed 
to 15° were solidified, that they were not destroyed ; and 
recently Mr. Buckton lias given us a note of seeing a 
young Bose Aphis batch out of its egg when the ther¬ 
mometer read at 25°. From this it does not appear 
as if we could depend on cold to rid us of insect-eggs. 
I am not aware of any series of observations having- 
been made as to the development of the eggs of our 
crop-insects, but from the enormous amount of details 
that have been published regarding Locusts by the 
Board of Agriculture of the American Government we 
may gain information of which the general principles 
may be of service to ourselves. 
Firstly, it is laid down as essential to excessive 
amount of Locust presence that the parent insects 
should be healthy, and the eggs properly deposited. 
These eggs are laid in masses seldom more than an 
inch below the surface of the ground. It has been 
found, by experiments carried on in natural circum¬ 
stances, that from the eggs buried two inches deep 
about a third of the young Locusts managed to make 
their way to the surface, but none from eggs placed at 
any greater depth.. Down to a depth of twelve inches 
the eggs hatched, and the young larval Locusts worked 
their way for an inch or two through the earth, but they 
were not able to pierce their way entirely through it, 
and at the time that these were hatched, eggs which 
were more deeply buried were still unhatched. Instances 
were also noted where hatching being retarded by the 
eggs being placed at a still greater depth, they lay there 
uninjured, and on being brought to the surface hatched 
at once. 
