OVIPAEISM. 
77 
both as to number and position. In some species from 
two to five are glued to a twig, whilst in others clusters 
are to be found composed of many hundred eggs. In 
Chermes laricis each egg is curiously pedunculated, 
as we see in Hemerobia, and arranged' in tufts covered 
with the cotton-like fibres torn from the back and sides 
of the parent. , 
The large size of the ova of the true Aphidince is 
worthy of remark ; they sometimes equal one half the 
length of the female herself. Thus she is incapable of 
carrying more than four or five in a forward state of 
development. There are; however, provisions for 
increasing this number, as the foremost ova are peri- 
odically expelled. 
Able experimenters have made interesting disco- 
veries as to the remarkable powers possessed by the 
fecundated egg of resisting intense cold without loss 
of its vitality. John Hunter exposed eggs of insects to 
a freezing mixture of ice and salt, and found that, 
although they solidified at 15° Fahr., they were not 
destroyed. Spallanzani, again, discovered no loss of 
vitality by a four hours’ exposure to a cold of 38° 
below zero, and even found that some eggs hatched 
after subjection to a cold of — 56°. Boerhaave noticed 
that the intense cold of the winter of 1709, in which 
the thermometer in France fell to the zero of Fahren- 
heit, in no ways reduced the number of the insects 
appearing in the following summer. Thus from 
numerous examples we are led to the conclusion that 
ova will, without destruction, bear a much lower 
temperature than the adult animals born from such 
ova. 
From facts like these, however, we must not assume 
that the intervention of cold weather is the only, or 
even the chief cause of the appearance of the perfect 
sexes in this family of insects. On the 12th of March, 
1873, whilst the thermometer marked 25° Fahrenheit, 
and snow was on the ground, I witnessed the hatching 
of a young Aphis from the eggs of SijphonopJiora rosce. 
