INTKODUCTIOK ii 



What renders the traBsformation the more remarkable is the brief 

 period in which it is commonly accomplished. The duration of the 

 pupa state varies very much, and development is greatly accelerated 

 by a high temperature and retarded by a low one. Among South- 

 African species the shortest time I have noted is in the case of the 

 common butterfly, Acrcea Horta, which remains only eight or nine days 

 in the chrysalis form during the height of summer, but in the winter 

 months of June and July is twenty-four days developing. As a rule, 

 the smaller species produce the perfect insect much sooner than the 

 large ones. The summer brood of Papilio Dcmohus is from twenty- 

 one to twenty-four days in the pupa state, but the oflspring of this 

 brood remain pupae from April to September or October. Instances 

 are, moreover, not rare in which certain individuals do not complete 

 their development simultaneously with the rest of the brood, but 

 remain arrested until the corresponding season of the next year, 

 notwithstanding that all the conditions of food, temperature, &c., may 

 have been identical as respects the entire brood. That this " standing 

 over " until next season of a certain number of the year's brood must 

 be of advantage to the species concerned can scarcely be doubted, but 

 in what way it is brought about has not, to the best of my knowledge, 

 been explained. 



When the Imago, or perfect insect, of the lepidopterous Order 

 makes its appearance from the cracked skin of the pupa, all its organs 

 are completely developed with the exception of the wings. The latter 

 are short, thick, and much folded or wrinkled, but exhibit in miniature 

 the colouring and marking proper to the species. They consist of two 

 separate membranes, upper and under, and are traversed by hollow 

 horny nervures situated between the two membranes. The insect 

 climbs to some situation where it can cling with the little moist 

 crumpled wings hanging freely downward, so that they can gradually 

 expand without obstruction, — a process effected by the steady extension 

 of the nervures. The elongation and stiffening of the latter tubular 

 organs seems to be due to their distension by introduced air, and partly 

 also by the entrance of fluid matter from the body. As the membranes 

 become stretched and tense they approach each other and finally 

 coalesce. This growth of the wings to their full extent is aided by 

 slight movements of the insect in turning from one side to the other, 

 or partly spreading the wings. Except in some of the largest species 

 the process is not of long duration, a few minutes sufiicing in the case 

 of the smaller Butterflies,^ while in some of the largest Moths I have 

 known it to occupy five or six hours. 



The Lepidoptera surpass all the other Orders of Insects in the 

 immense size of their wings in comparison with that of the body. 



^ One of the larger South-African Butterflies, a female Diadema Misippus, which I 

 timed from the moment of its complete extrication from the chrysalis, was exactly fifteen 

 minutes in acquiring the full expansion of the wings. 



