62 ON PLANTS AND INSECTS. [LECT. 



instructive. The caterpillar of the euphorbia hawk-moth 

 begins life of a clear green colour, 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 

 have seen, were only very gradually assumed. In the 

 third stage, the line has disappeared, leaving the white 

 spots. In the fourth, the caterpillars have become very 

 variable, but are generally much darker than before, and 

 have a number of white dots under the spots. In the 

 fifth stage, there is a second row of white spots under 

 the first. The caterpillars not being good to eat, there 

 is, as has been already pointed out, no need for, or 

 attempt at, concealment. Now, if we compare the 

 mature caterpillars of other species of the genus, we 

 shall find that they represent phases in the development 

 of Deilephila euphorbia. D. hippophae, for instance, 

 even when full grown, is a plain green, with only a 

 trace of the line, and corresponds, therefore, with a very 

 early stage of D. euphorbia; D. zygopliylli, of South 

 Eussia, has the line, and represents the second stage of 

 D. euphorbia ; D. livornica has the line and the row 

 of spots, and represents therefore the third stage ; 

 lastly, D. vespertilio and D. galii have progressed further, 

 and lost the longitudinal line, but they never acquire the 

 second row of spots which characterizes the last stage 

 of D. euphorbia. 



Thus, then, the individual life of certain caterpillars 

 gives us a clue to the history of the species in past 

 ages. 



For such inquiries as this, the larvae of Lepidoptera 



