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has the appearance of a single thread. The skin now splits at the neck, 

 and is stripped off by twistings of the body, leaving the pupa in a sus- 

 pended condition. 



3. The Pupa. — This is a greenish-yellow object with black dots 

 and numerous angles and edges, so that, as a rule, it is not very easily 

 remarked. (Nevertheless, the sharp-sighted titmice manage to dispose 

 of a great many of these pupae.) Portions of the future butterfly may, 

 indeed, be distinguished on the hard envelope of the pupa, but the limbs 

 are never free, as is the case of the pupse of beetles and hymenopterous 

 msects (which see). The pupa thus remains suspended in an apparently 

 lifeless state throughout the winter. Life, however, is not extinct in its 

 internal organization, for there the butterfly is gradually developed. 



4. Let us inquire into the meaning of this pupal sleep. Very powerful 

 changes must take place in the structure of the pupa in order to convert 

 the sluggish, plant - feeding caterpillar into the swift - winged, honey- 

 sucking butterfly. If the animal, therefore, were active during the 

 pupal stage, a large quantity of the stored-up food material would be 

 used to no purpose (motion, like every other kind of work, being connected 

 with the consumption of material, see Part I., p. 7), and this quantity 

 would therefore be withdrawn from the processes of metamorphosis. 

 (For the same reason we meet with quiescent pupal stages in all insects 

 whose larvffi live under totally different conditions from those of the 

 mature insect, and are accordingly also of an entirely different structure 

 to the latter. Compare, on the other hand, insects with incomplete 

 metamorphosis, e.g., grasshopper.) 



D. Butterfly. 



In spring, when Nature has once more returned to life, the now fully- 

 matured butterflies burst through their pupal shroud (a symbol of the 

 resurrection), soar aloft into the balmy air, and feast upon a richly-laden 

 banquet of flowers. These tender creatures live, however, at most but a 

 few weeks, dying, like all other insects, soon after they have provided for 

 the continuation of the species. The cabbage butterflies, therefore, which 

 disport themselves in the air from July to autumn are not the first brood, 

 but their offspring. They have passed through their larval stage, feeding 

 upon all kinds of wild cruciferous plants, and have passed through a 

 pupa stage just like their parents, except that, on account of the high 

 temperature of the summer season, they have quitted the pupal condition 

 as perfect insects in the course of a few weeks. Thus, the cabbage 

 butterfly has two broods (or generations) annually ; the second of these, 

 having been developed under vastly more favourable conditions (how 

 so ?), is on that account much more numerous than the first. 



