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 larvae of Ephemeridaa 

 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 role 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 larvaa of Ephemeridaa 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 larvae of Ephemeridas at a time when 110 

 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. 



