22 
“ plumules ” have much to do with rendering their male 
owners more vigorous on the wing, for I have generally- 
found the rule to be greater activity and speed among the 
females. The markings, too, are very varied ; and though 
much has been done in this direction, much more remains 
to be worked out. The last point has reference to the way 
in which the wings expand and the scales are drawn out 
when an insect escapes from the pupa case. Some have 
thought that each scale expanded in size along with the wing- 
membrane itself, the air breathed by the newly developed 
insect entering between the two laminae, and causing their 
enlargement ; others, that they depended on the age and 
vigour of the insect ; in fact, being small in the newly deve- 
loped, and of full size in one of mature age — assuming, what 
is not the case, increase in size as the insect becomes older. 
If a portion of that part of the pupa case which covers the 
Avingbe removed a day or two before an insect escapes, it will 
be found the scales are all of full size ; or if a wing of a newly 
escaped insect be taken before the wing has time to expand, 
it will be seen that the scales are not only of full size, but 
packed closely together both laterally and longitudinally, as 
fig. 20. As the wing-membrane expands, the rows of scales 
are drawn further and wider apart, until they present the 
appearance seen in a fully r - developed wing (fig. 21). There 
is, therefore, literally no growth of scales after the insect 
emerges from the pupa case, but simply a lateral and longi- 
tudinal opening out, or double telescopic unfolding of the 
wings. Fig. 22 represents the actual size of the wing of the 
large white P. brassiere when emerging from the pupa case ; 
fig. 23 shows the full-sized wing of the same butterfly. An 
analogous state of things is seen in the leaves of some plants 
having scales or hairs, notably in the case of the Deutzia 
scabra, whose stellate scales are well known. If one leaf of 
an unexpanded bud be removed, the stellate scales will be 
found of full size, but so crowded as to completely cover the 
leaf ; if either a fully-formed leaf be taken, or the leaf oppo- 
site to that removed be allowed to grow, the scales will be 
found not to have increased in size, but only to be more widely 
separated by the lateral and longitudinal expansion of the 
leaf itself. 
