560 
BIONOMIC NOTES 
is fulfilled in Europe during some part of every day near midsummer, 
and in the tropics during some part of every day in the year. 
When the butterfly is upright its shadow is nearly as long as 
its wings, and is fully exposed to view (see Fig. 16). 
Fig. 16.—Shadow of butterfly—upright. 
If the butterfly were to list towards the sun its shadow, still 
fully exposed to view, would diminish until the list became equal to 
the sun’s altitude, when there would be no shadow. In this position, 
moreover, its wing surfaces would be least illuminated. 
Supposing the butterfly to increase its list; this would bring the 
sun’s rays on to the under surface of its left wings and so throw 
Fig. 17.—Shadow of butterfly—listing 65° towards sun. 
the shadow to the right, or towards the sun (see Fig. 17). The 
shadow would continue to increase in length until, when the butter¬ 
fly’s wings touched the ground, it would equal them in length. On 
the other hand, as the shadow increased in length it would be more 
and more concealed from view. 
