NO. lO 



TROPISMS OF LEPIDOPTERA McINDOO 



13 



Larvae of the fifth instar sometimes acted indifferently to light 

 (fig. I, D, No. 108) hut generally were weakly photonegative (Nos. 

 102, 118, 126, I2p). Larvae of the sixth instar were either weakly 

 (fig. I, E, No. 100) or strongly photonegative (Nos. 34, 68, 72, /j, 

 78), the degree depending on their age. In all cases they oriented 

 quickly and moved hurriedly from the light as illustrated in figure i, E. 



D F 



Fig. I. — Tracings of phototactic responses of codling-moth larvae (see p. 12 

 for further explanation) . A, Movements of recently hatched larvae of first 

 brood tested on table betv^-een an east and a south window at 3.45 P. M. B, Re- 

 cently hatched larvae of second brood tested in phototactic box. C, Larvae of 

 second brood ; Nos. 112 a and h, fourth instar ; Nos. lis « and h, third instar ; 

 and Nos. 124 a and b, second instar. D, Larvae of second brood, fifth instar. 

 E, Larvae of second brood, sixth instar, fully grown. F, Fully grown larva, 

 No. IS4, ready to spin ; a and b, normal ; c to /, ocelli blackened. 



Normal larvae of the sixth instar, ready to spin cocoons, were 

 strongly photonegative (fig. i, F, No. 154a and b), but when their 

 ocelli were covered with a mixture of glue and lamp black they became 

 indifferent to light as illustrated in figure i, F, c to /. 



One of Loeb's early observations indicated to him that lepidopterous 

 larvae do not generally react to geotaxis, but that this tropism is 

 replaced by phototaxis. According to Lammert (40), Schmitt- 

 Auracher, after finding a migration of pigment in the ocelli of insects, 

 supported this view and then assumed that the ocelli were capable of 



