382 Studies in the Theory of Descent. 



a ribbed leaf, others of the longitudinally striped 

 species became developed in another manner. 



Some of the latter lived indeed on bush-like 

 leaved plants, but no oblique stripes were de- 

 veloped, because these would have been useless 

 among the dense, narrow, and feebly-ribbed leaves 

 of the food-plants. These caterpillars, from the 

 earlier markings, simply retained the longitudinal 

 lines, which, combined with a very close resem- 

 blance to the colour of the leaves, afforded them a 

 high degree of protection against discovery. This 

 protection would also have been enhanced if other 

 parts of the food-plant, such as the berries (Hip- 

 pophaes), were imitated in colour and position in 

 such a manner that the large body of the caterpillar 

 contrasted still less with its environment. In this 

 way the first ring-spot probably arose in some 

 species on only one the penultimate segment. 



As soon as this first pair of ring-spots had be- 

 come an established character of the species, they 

 had a tendency to become repeated on the other 

 segments, advancing from the hind segments 

 towards the front ones. Under certain conditions 

 this repetition of the ring-spots might have been of 

 great disadvantage to the species, and would there- 

 fore have been as far as possible prevented by 

 natural selection (HippophaZs) ; in other cases, how- 

 ever, no disadvantage would have resulted the 

 caterpillar, well adapted to the colour of its food- 

 plant, would not have been made more conspicuous 



