CHAPTER IL 
WINTERING AND HATCHING THE EGGS. 
As has been said in the last chapter, the egg of the Silk-worm changes 
color soon after oviposition. During this operation the contents undergo 
a chemical change, absorbing oxygen and giving off carbonic acid. This 
absorption of oxygen is very active during the first six days, after which 
it rapidly declines and continues at a very low rate during the months 
which precede hatching. The eggs should, therefore, be wintered in 
such manner that they have plenty of air; otherwise their development 
will be seriously interfered with. They must not be packed in thick 
layers, but should be spread out thinly. For these reasons the eggs at 
this Department are kept through the winter in boxes of perforated 
tin, the bottoms of which have a surface of 64 square inches, each box 
containing not more than one quarter of an ounce of eggs. 
The atmosphere in which the eggs are kept should neither be too dry 
nor too humid. M. Beauvais found a saturation of 50 per cent. to be the 
most suitable condition of the air, as when it is below that point the 
liquids of the eggs evaporate so rapidly as to require a highly saturated 
atmosphere for theirincubation. Excessive moisture, on the other hand, 
will assist the formation of mold, which will quickly injure the contents 
of theegg. The eggs should be frequently inspected, and whenever such 
mold is discovered it should be quickly brushed off and the eggs re- 
moved to a drier locality. 
Under natural conditions the egg undergoes a partial development as 
soon as laid, as shown by its changing color. After oviposition, and un- 
til subjected to cold, the eggs of the annual races are not capable of 
hatching out. This is the rule, although we often find in a batch of an- 
nual eggs a few accidental bivoltins that hatch some fifteen days after 
they are laid. The number, however, is very slight, and it has been 
determined that the temperature to which they are submitted in no way 
alters the result. During this period, which we call prehibernal, the 
eggs may be kept at any ordinary temperature, however warm, but once 
they are submitted to the cold of winter a certain change takes place in 
them, the nature of which has not yet been determined, and their sub- 
sequent warming may then result in hatching. As in our climate warm 
days are quite frequent in late winter, it 1s very necessary that the eggs 
be kept below the hatching temperature until the foliage on which the 
worms are to feed is developing and all danger from late frosts is at an 
end. The period of hibernation may be lengthened by keeping the eggs 
in a cool, dry cellar, with a northerly exposure, and in general tiis will 
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