126 THE DARWINIAN THEORY 



i. Larval Insects. — Lepidopteran larvae, or cater- 

 pillars, are in the great majority of cases absolutely 

 defenceless : their bodies are soft and their very 

 shape is due to their containing fluid under pressure, 

 therefore a slight wound involves much loss of fluid 

 or blood ; hence their great need for protection. 

 The great purpose in life of a caterpillar, next to 

 feeding, is not to be seen, or rather not to be re- 

 cognised. 



General protective resemblances are found in their 

 green colour, which is the most usual, and harmonises 

 with that of the food-plant. This green colour is 

 partly due directly to food and partly to metachloro- 

 phyll, a special pigment in the blood, and a slightly 

 altered derivative of the chlorophyll of the food. 

 Those caterpillars which have the habit of feeding 

 either on grass, or on low-growing plants among the 

 grass, are protected by longitudinal striping. In the 

 larger caterpillars, such as those of the Privet hawk 

 moth, which are striped transversely or obliquely, 

 the colour is usually that of the flower of the food- 

 plant, and the stripes serve to break up the surface 

 of the body. These larvae turn brown at the time of 

 descending to the earth to change into pupae. 



Special protective resemblances are best seen in the 

 larvae of the geometer moths, or " stick caterpillars " 

 as they are called. These are very common, and are 

 rarely seen, or rather detected, owing to their re- 

 semblance to twigs. They have only two pairs of 

 legs or claspers, a long thin and cylindrical body, 

 which stands out at an acute angle with the stem 

 upon which they fix themselves, and upon which 



