HELIOTROPISM or AXIM\I,S (.', 



liehavior of an animal is merely the rcxnlttiiil of all i/s 

 forms of irri/<i/>ili///. and so it may happen that an animal 

 is positively heliotropie even when it has no opportunity to 

 make use of it. The Iarvo3 of many saw-flies behave just as 

 the caterpillars of Lepidoptera. I have made observations 

 mi the larviB of Nematus ventricosus, which are exactly like 

 those on Porthesia chrysoirhoea, which have been described. 



I have not yet succeeded in demonstrating a heliotropie 

 reaction to diffuse light in the indigenous pupae. Wilhehn 

 Miiller, however, has observed effects of light in South 

 American species. 1 The pupa? can move at three joints. 

 ( )nlv a lateral movement to the right and left is possible in 

 some of the species; in other species only a dorsal move- 

 ment of the body is possible; in a third species of pupa3 a 

 combination of both kinds of movements is possible. Miiller 

 observed that all three classes of movements can be brought 

 about under the influence of light. He found that some 

 pupa3 turned not only away from the light, but also toward 

 it. He also found that when the animals had been exposed 

 to the dark for some time, they "needed some time to become 

 susceptible again to the influence of light.'' In interpreting 

 the phenomena Miiller follows the Darwinian idea, so that 

 the thought never occurs to him that he might be dealing 

 with phenomena similar to the heliotropie phenomena of 

 plants. 



Tin- iK'tjdtirc </<'ofroi>ism of lite Lepidoptera. -The 

 movements of very young or recently hatched animals have 

 for the most part been misunderstood, because they have 

 always been considered a function of mysterious "instincts"' 

 of the animals, while the direction of their motions is in 

 reality determined by definite external forces. The same 

 cause which prescribes the course of a falling stone or deter- 

 mines the orbits of planets, namely gravitation, determines 



i Mf'LLER, Zooloyische JnltrliH,-ln:>; Vol. I ISM; . H>. "''>* II. 



