78 
BRITISH APHIDES. 
The young insect, when free, was lively, and began 
immediately to crawl about in search of its food. On 
December 29th of the same year I saw the birth, in 
the open air, of two young Aphides from the winged 
viviparous female of the same species. She had survived 
the intense cold of the previous night, in which the 
thermometer marked 13° Fahrenheit. 
Yiviparism continued uninterruptedly through the 
whole winter of 1874 and during the following spring; 
also I failed to discover a single oviparous female, or 
one egg of that species. The function of oviposition 
therefore seems to have little reference to the pre- 
servation of any particular species from the rigour of 
winter, as has been maintained by some entomologists. 
Some other cause must be sought for the completion 
of what may be styled the cycle of the compound 
individual, at which period there would appear to be a 
necessity for a fresh impetus from the male in order 
to perpetuate the species. 
The vitality of minute insects must strike us with 
astonishment. What can be the constitution of their 
living, organised juices, since they thus resist freezing 
into rigidity and death ? It may be assumed that their 
bodies cannot differ greatly in temperature from the 
surrounding air, yet their muscles and limbs remain 
supple and free for locomotion under these extreme 
conditions. It is certain that some insects are never 
torpid in winter. Thus Podura nivalis^ Linn., Boreas 
hyemalis, Latr., Chioneoj araneides, all run and live on 
the snow. At the other extreme of temperature we 
have the little entomostracian Cypris^ which, after many 
weeks^ baking in the hot sun, will recover its activity 
on being restored to its pool of water. 
To give a general idea of the growth of an Aphis 
from its exclusion out of the egg to the development of 
the true male and female sexes, it will be well to confine 
the description here to one species, and the common 
insect Siphonophora rosce may be taken, as it is persist- 
ent throughout the year, and is a familiar form. 
