COCKROACHES, ETC. 149 



attitude, i.e. turned so as to catch the full strength of 

 sun-rays, which for it are practically non-existent, 

 while at night the plant adopts the sleeping attitude 

 even if the room be brightly lit. In fact, all attempts 

 to turn the plant's and the Stick-Insect's nights into 

 days, and days into nights, are a failure. The in- 

 herited rhythm of action is much stronger than the 

 suddenly reversed stimuli of light and dusk ; the Stick- 

 Insect will rest and the plant will wake in the day in 

 spite of artificial darkness, and conversely at night in 

 spite of brilliant illumination. 1 



Most of the winged species of Phasmidce, especially 

 some with brightly coloured wings, are diurnal feeders, 

 or at 'any rate feed as readily during the day when 

 in captivity as during the night. Dr. Annandale has 

 stated that during the great heat of the day in Malayan 

 jungles, when insectivorous birds are not actively hunt- 

 ing their prey and when all nature seems to be at 

 rest, gasping in the heat, Stick- Insects are apparently 

 more abundant because they are more on the move 

 than early in the morning or towards the close of 

 day. I do not know if Dr. Annandale is referring only 

 to winged species : for my own part I have always 

 found the most stick-like apterous forms very difficult 

 to find at any time of the day [Note n, p. 315]. 



1 The results described are probably due to the persistence 

 of an individual rhythm already set up, and not to an inherited 

 specific rhythm. In order to prove the existence of the latter 

 it would be necessary, to begin the experiment very early in life, 

 before any individual rhythm can have been set up. A note at 

 the end of this chapter shows that the author had intended to 

 refer to Sir Francis Darwin's Presidential Address to the British 

 Association (Report, 1908, p. 3), where the inheritance of acquired 

 characters is supported on similar grounds. E. B. P. 



