298 THE WONDERS OF INSTINCT 



green stuff before finishing the ritual repast whereat 

 skin bottles furnish forth the feast. It is the first time 

 that I have seen a larva make a meal of the sack in 

 which it was born. Of what use can this singular fare 

 be to the budding caterpillar? I suspect as follows: 

 the leaves of the cabbage are waxed and slippery surfaces 

 and nearly always slant considerably. To graze on them 

 without risking a fall, which would be fatal in earliest 

 childhood, is hardly possible unless with moorings that 

 afford a steady support. What is needed is bits of silk 

 stretched along the road as fast as progress is made, 

 something for the legs to grip, something to provide a 

 good anchorage even when the grub is upside down. 

 The silk-tubes, where those moorings are manufactured, 

 must be very scantily supplied in a tiny new-born animal ; 

 and it is expedient that they be filled without delay with 

 the aid of a special form of nourishment. Then what 

 shall the nature of the first food be? Vegetable matter, 

 slow to elaborate and niggardly in its yield, does not 

 fulfil the desired conditions at all well, for time presses 

 and we must trust ourselves safely to the slippery leaf. 

 An animal diet would be preferable : it is easier to digest 

 and undergoes chemical changes in a shorter time. The 

 wrapper of the egg is of a horny nature, as silk itself 

 is. It will not take long to transform the one into 

 the other. The grub therefore tackles the remains of 

 its egg and turns it into silk to carry with it on its first 

 journeys. 



If my surmise is well-founded, there is reason to believe 

 that, with a view to speedily filling the silk-glands to 



