72 MARVELS OF THE ANIMAL WORLD 



which indulges in the practice of laying her eggs 

 around the twig of a tree in the form of a bracelet, 

 as many as three hundred being glued together in 

 this manner by a hard substance, somewhat 

 resembling varnish, which serves to protect them 

 against the rigour of the weather. 



That insects' eggs are capable of withstanding 

 a great degree of cold without resulting in injury 

 to their well-being is proved by experiments that 

 have been made upon them, one writer recording 

 the fact that he enclosed some eggs of the silk- 

 worm moth in a glass receptacle which he placed 

 in a mixture of rock-salt and ice for a period of 

 five hours, when the temperature fell to six degrees 

 below zero. Notwithstanding this severe treatment, 

 the eggs hatched out during the following spring 

 at just the same time as some others which had 

 not been thus treated. The same writer continued 

 his experiments on a subsequent occasion, and put 

 some more eggs to a far more severe test. He 

 states : ' A mixtmre of ice and rock-salt, with the 

 burning spirit of nitre, reduced the thermometer 

 22 degrees below zero . . ., or 52 degrees lower 

 than the point at which water freezes. They were 

 not injured, as I had evident proof — by their being 

 hatched.' 



The incubation period of eggs varies considerably, 

 in some cases being very rapid, while in others 

 some time elapses before the process is completed. 

 The eggs of the common house-fly, for instance, 

 wiU, under favourable conditions, hatch out within 

 eight hours after being deposited by the female ; 



