214 THE COLOURS OF ANIMALS 



shall recognise and avoid the larvae in which it has 

 laid its eggs. When the eggs are laid within the body 

 of a caterpillar the skin is pierced, and a small amount 

 of blood exudes and generally forms a black clot. 

 These black spots are probably recognised by other 

 parasites, and the larva is consequently avoided. 

 Although the spots would disappear after a change of 

 skin, the parasites generally lay their eggs at about 

 the same period of larval growth, and would be 

 warned over a considerable part of this period. Al- 

 though these are not, properly speaking, Eecognition 

 Markings, we shall see that they form the foundation 

 on which such characters have arisen. 



Other parasites (among the Hymenoptera), such as 

 those of the genus Paniscus, lay eggs upon the body of 

 their prey. The eggs are pear-shaped, and are firmly 

 fixed by the stalk, which is knobbed at the end. So 

 tightly do the eggs adhere that the caterpillar can change 

 its skin without removing them (see pp. 275-77). 

 Several eggs are fixed upon a large caterpillar, two 

 or three upon a small one, although the number varies 

 greatly in different individuals. 



These external eggs are black and shining, and 

 they are very conspicuous against the colour of the 

 caterpillar, which is generally green. When Professor 

 Weismann was staying with me in the summer of 

 1887, 1 showed him a larva of the Puss Moth (Cerura 

 vinuLa) to which several eggs were attached. This led 

 to a discussion as to the meaning of the colour, in 



