365 
the skin, which along the wing-border fold over into each other. 
When we imagine this fold to become repressed up to the first 
initial rudiment of its evolution, then these lamellae do not extend 
horizontally along parallel planes in contact with each other, but 
quite the contrary lie in one and the same dorsoventral plane. 
When in applying this mode of representation of the wing we look 
at it from the side, it is seen projected on the lateral body-wall, 
and so each wing can be drawn as a sexangle, which by its hori- 
zontal diagonal is divided into a dorsal half (the upper wing-surface) 
and a ventral one (the underside of the wing): the diagonal itself 
representing the wing-border. That by this projection-method the 
wing-field appears extremely small in relation to the dimensions of 
the body, need not according to my view be considered as a real 
objection against it. For the relation in size between wings and 
body in different species of Lepidoptera varies between very wide 
limits, and in the females provided with rudimentary wings of 
sundry species it even approaches the schematic condition described. 
Likewise during the pupal stage of almost all kinds of Lepidoptera 
the wings are far smaller than after the emersion from the nymphal 
sheath. 
This projection of both wing-surfaces upon the dorso-ventral 
plane sharply draws our attention to the fact that markings, which 
on the wall of the body stretch in an oro-aboral direction, will run 
in a so-called transversal one over the wing-surface, i. e. from the 
anterior towards the posterior wing-border. The dorso-ventral com- 
ponents of the pattern on the contrary will traverse the wing-field 
from root to external margin (commonly called longitudinally). In 
the same way this method can give support to the belief, that the 
pattern of the upper surface need not originally have been identical 
with that of the underside, as they correspond to different, though 
neighbouring areas of the sidewall of the body. 
Finally this way of representing the wings as projected on the body 
highly facilitates and accentuates the comparison with the caterpillar. 
To get a pure comparison with the pupa however, we are obliged 
somewhat to modify the position and the size of the sheath of the 
forewing, which involves the formation of an empty space towards 
the side of the abdomen, corresponding to the place where the hind- 
wing would have been situated, when this were visible on the pupa. 
In order to insert the real wing-pattern into these schematic 
sexangles, we have to project it upon them. To do this, we must 
turn the wing obliquely up- or downwards and draw a contracted 
image of its colour-pattern on the perpendicular plane of projection. 
24* 
