INTRODUCTIOK 
II 
Wliat renders the transformation 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, Acrcca 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 Pa'pilio Demoleics is from twenty- 
one to twenty-four days in the pupa state, but the ofispring of this 
brood remain pupse 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 sufficing 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. 
