60 ON PLANTS AND INSECTS. [LECT. 



so many other caterpillars, and gradually acquire a 

 succession of markings, the utility of which I have 

 just attempted to explain. The young larva, in fact, 

 represents an old form, and the species, in the lapse of 

 ages, has gone through the stage which each individual 

 now passes through in a few weeks. Thus the cater- 

 pillar of Charrocampa porcellus, the small elephant hawk- 

 moth, a species very nearly allied to Ch. elpenor, passes 

 through almost exactly the same stages as that of Ch. 

 elpenor. But it leaves the egg with a subdorsal line, 

 which the caterpillar of Ch. elpenor does not acquire 

 until after its first moult. No one can doubt, however, 

 that there was a time when the new-born caterpillars of 

 Ch. porcellus were plain green, like those of Ch. elpenor. 

 In this respect, then, Ch. porcellus is a newer specific 

 form than Ch. elpenor. Again, if we compare the 

 mature caterpillars of Chcerocampa, we shall find 

 there are some forms, such as Ch. myron and Ch. 

 chcerilus which never develope eye-spots, but which, 

 even when full grown, correspond to the second stage of 

 Ch. elpenor. Here, then, we seem to have a species still 

 in the stage which Ch. elpenor must have passed 

 through long ago. 



The genus Dailephila, of which we have in England 

 three species the euphorbia hawk-moth, the galium 

 hawk-moth, and the rayed hawk-moth is also very 

 instructive. The caterpillar of the euphorbia hawk-moth 

 begins life of a clear green color, without a trace of 

 the subsequent markings. After the first moult, how- 

 ever, it has a number of black patches, a white line, 

 and a series of white dots, and has, therefore, at one 

 bound, acquired characters which in Ch. elpenor, as we 



