MODELS, MIMICS AND INTERMEDIATES 267 



showed very little variation, as may be seen from the 

 table. 



But to my great astonishment, when I returned to 

 the same islands after the war, the situation had been 

 completely reversed, and the Pseudacraeas, which showed 

 much variation, greatly outnumbered the Planemas 

 (see table, p. 265). It must be supposed that the 

 Planemas had been found at the summit of a wave of 

 prosperity in 1914, but that their enemies (possibly 

 parasites) had increased so greatly that they in turn 

 reached the summit of a wave while the Planemas fell 



into a trough. This would be analogous to what is known 

 to happen in England in the case of the Hop Aphis and 

 the Ladybirds which feed upon them, each in turn 

 fluctuating in number. 



It is most interesting to note how the Pseudacraeas 

 changed in constancy, the intermediate forms having 

 been apparently destroyed while the models exercised 

 their protection to the mimetic forms in 1914, but 

 having an equal chance of survival in 1918-19 when 

 the protection of the models was in abeyance. Young 

 birds in 1914 had a different lesson to learn from 



