296 THE WONDERS OF INSTINCT 



are, on the contrary, rare. The mother's output is 

 affected by the degree of quietness at the moment of 

 laying. 



The outer circumference of the group is irregularly 

 formed, but the inside presents a certain order. The 

 eggs are here arranged in straight rows backing against 

 one another in such a way that each egg finds a double 

 support in the preceding row. This alternation, without 

 being of an irreproachable precision, gives a fairly stable 

 equilibrium to the whole. 



To see the mother at her laying is no easy matter: 

 when examined too closely, the Pieris decamps at once. 

 The structure of the work, however, reveals the order of 

 the operations pretty clearly. The ovipositor swings 

 slowly first in this direction, then in that, by turns; and 

 a new egg is lodged in each space between two adjoining 

 eggs in the previous row. The extent of the oscillation 

 determines the length of the row, which is longer or 

 shorter according to the layer's fancy. 



The hatching takes place in about a week. It is almost 

 simultaneous for the whole mass: as soon as one cater- 

 pillar comes out of its egg, the others come out also, 

 as though the natal impulse were communicated from 

 one to the other. In the same way, in the nest of the 

 Praying Mantis, a warning seems to be spread abroad 

 arousing every one of the population. It is a wave 

 propagated in all directions from the point first struck. 



The egg does not open by means of a dehiscence 

 similar to that of the vegetable-pods whose seeds have 

 attained maturity; it is the new-born grub itself that 



