108 
BRITISH APHIDES. 
Balbiani to result from fecundation. Previous to this 
time the outer coats are sufficiently thin and trans- 
parent to allow the process of segmentation to be 
observed. 
The ovum measures about one half the length of the 
body. 
The specimen drawn, Plate II, fig. 5, was taken 
with several others on December 5th, when the 
thermometer marked 24^ Fahr. Several eggs were laid 
by them a few days after their capture. Whilst under 
a microscopic examination one female was watched 
during the process of glueing her eggs to a twig. The 
tenacious glutinous coat could be drawn into threads 
on rolling the same upon a strip of glass. 
Notwithstanding the great size of the ovum the 
female may carry five or more. These, however, are 
not equally large, but are found to vary in bulk as they 
approximate maturity and the time for expulsion. 
On the Progressive Grotvth of Siphonophora rosce. 
Only three marked periods of metamorphosis are 
usually recognised amongst insects. Nevertheless, it 
is probable that minute modifications of structure, 
both external and internal, ensue at each moult. 
Such moultings are generally very numerous 
amongst Aphides. Independently of these castings of 
the exuvise there can be no question of a slow 
progression towards the perfect insect, which change 
becomes very obvious if we compare the insect just 
hatched from the egg with the young just born alive 
from any of the later broods. The young born late in 
autumn are singularly different from those born in 
early spring, and they may be looked upon as more 
highly developed. To give a better representation of 
these changes several figures may be found in Plates I, 
II, III, and IV, which have been made by the camera 
lucida. 
This well-known species of Aphis infests several 
