182 TEANSACTIONS LIVEEPOOL BIOLOGICAL SOCIETY. 



yet because of their minute size and curiously spasmodic 

 appearances and disappearances make the investigation 

 of their occurrences, and more especially of their non- 

 occurrences, all the more difficult. 



For instance, whether or no the beaver is now extinct 

 in the British Islands, there can hardly be too opinions. 

 Scarcely the most persistent optimist can cherish the 

 hope that the great copper butterfly will ever again be 

 seen of mortal eyes in the eastern fens ; but what amount 

 of negative evidence is sufficient to justify the assumption 

 that such and such a species of Homalota or Atonaria 

 does not occur in any particular locality. A single pro- 

 perly verified record is sufficient to establish the positive 

 side, but as the proof of the negative is proverbially a 

 hard matter, so in a case where the subjects are so 

 minute and so elusive, it verges on the impossible. 



Furthermore, there is an even still more perplexing 

 factor in the problem, and that is what I have just alluded 

 to as the spasmodic method of appearance of so many 

 insects. This is a very interesting subject, and very 

 worthy of more attention and investigation than it has 

 yet received. The extraordinary irregularity of such an 

 insect as the hawk moth, Deilephila galii, is a case in 

 point, but the characteristic prevails more or less among 

 all insect life. 



Doubtless the meaning of such phenomena is to be 

 found in the singular delicacy of adjustment between 

 insects and their environment, so that the most minute 

 and obscure change in the latter is responded to in a 

 greatly enhanced and apparently exaggerated degree by 

 the former, although the connection may be quite unknown 

 to us, and often indirect. 



But I firmly believe that a large proportion of what is 



