44 STUDIES IN GENERAL PHYSIOLOGY 
also the path which a butterfly follows that has just emerged 
from the pupa case. The geotropic irritability is at that time 
especially strong; the newly hatched animals remain restless, 
and are compelled to run about until they come to a vertical 
wall, on which they can put the longitudinal axes of their 
bodies vertically, with their heads upward. Here they remain 
quietly until their wings are unfolded. The powerful mani- 
festation of negative geotropism at the time of hatching is 
no isolated phenomenon in insects. In summer we find 
great numbers of the ecdyses of the larve of Ephemeride 
on the banks of streams. They are found on blades of grass 
or steep banks, with their longitudinal axes usually vertical 
and the head upward. That gravity, and not light alone, 
plays the chief réle here is shown by the fact that I have 
found the ecdyses in the same position under bridges where 
no light could strike them from above. 
This observation on the larvee of Ephemeride makes it 
impossible for us to accept the idea that the “purpose” of 
the orientation of the freshly hatched imago of a butterfly 
is that the wings may unfold; for negative geotropism 
appears in the larvee of Ephemeride at a time when no 
wings are present. The caterpillars of butterflies are also 
negatively geotropic like the freshly hatched moths, even 
though not so markedly. Immediately after hatching geo- 
tropism is much stronger in the imago of the butterfly than 
heliotropism—a phenomenon rarely observed in the animal 
kingdom. If a freshly hatched imago is on a vertical wall, 
it does not change its orientation toward the center of 
gravity even when the direction, refrangibility, or intensity of 
the light is changed. 
What is true of the heliotropism of Lepidoptera, that it 
is most marked during certain periods of their existence, 
holds good also for their geotropism. Amphipyra is ener- 
getically negatively geotropic immediately after moulting. 
Digitized by Microsoft® 
