332 



Mr. Poulton's ^/)rrf//cr experiments upon 



but mostly very rough ; 1 was curved, the rest straight. 

 The relation between the sizes of twigs and the smaller 

 glass cylinder first used is shown about } the real size in 

 Plate XV., fig. 4.^ ^ 



In the comparison experiment, '25 larvse were intro- 

 duced July 20 into a glass cylinder (about 185 mm. high, 

 82 mm. internal diameter, and 1000 cc. capacity) ; and 

 on Aug. 21 they were transferred into two lamp-shades 

 (about 165 mm. high, and the approximate capacity of 

 1300 cc). These larvae were treated exactly as in the 

 former experiment, except that their surroundings were 

 uniformly green, no dark twigs being at any time ad- 

 mitted. The results of the experiments are given below. 



ExPEEUrENT IV. 



Green Surroundings, with very 

 small proportion of dark material. 



Experiment V. 

 Green Surroundings alone. 



July 20. — 25 larva) introduced. 



Aug. 12. — 8 larvR! were resting on 

 the pieces of dark stick, and 1 was 

 holding a piece by its thoracic legs. 



Aug. 21. — 23 larviiD alive; shifted 

 to larger lamp-shade. 



Aug. 24. — The larva? compared (1 

 unnoted) : — 



Intermediate . . 

 Green .... 4 

 Dark .... 12 



22 

 Aug. 26. — 1 dark larva dead (about 

 half -grown in last stage). 



Aug. 30. — 6 larva) dead : — 4 dark 

 (1 large, 3 small in last stage) ; 

 2 fireen (small in last stage). 

 The rest carefully compared : — 



Green 3 



Greeiihh intermediate . 2 

 Intermediate .... 1 

 Brownisli intermediate . 2 

 Bark 8 



16 



Sept. 2. — The larvre were now 

 mostly pupating ; 1 had died, and 

 1 was lost. No further change in 

 the colours. 



July 20. — 25 larvas introduced. 



Aug. 21. — 22 larvas alive; shifted 

 to two lamp-shades, between which 

 they were equally divided. 



Sept. 2. — Many were now pu- 

 pating; all the 22 were alive, and 

 all bright green. 



These results are very interesting and remarkable. 

 They show that the susceptibility to dark surroundings 



