SILK-WORMS. 
233 
impregnated ones, I have found that they have 
formed the seventh or eighth part of them. 
That was particularly the case in 1813 ; the 
temperature was 62°, 64°, GG°, during almost the 
whole time of the collection of the cocoons, and 
even after that the eggs burst. In a similar case, 
the means which I have described above ought to 
be adopted, in order to obtain a more suitable tem- 
perature. Sometimes it happens also that some 
female moth escapes from its mate before impreg- 
nation, which produces many unimpregnated 
eggs- 
Eight or ten days after the deposition of the 
eggs, the jonquil-colour, which is peculiar to 
them, becomes deeper, then changes into a red- 
dish gray, and afterwards into a pale clay-colour. 
All these changes of colour come from the fluid 
of the eggs, and not from the shell, w r hich is 
almost transparent. (Chap. V.) 
Whether the eggs be not at all impregnated, 
or only imperfectly so, they are always of a 
lenticular form. A little time after their pro- 
duction, there takes place, in the centre of both 
surfaces, a depression, which proves that a portion 
of the aqueous part of the egg has been disengaged, 
and that a kind of drying process has been 
effected. There is scarcely any difference of 
weight between impregnated eggs. (Chap. V. 
§ 3.) 
