SENSES OF INSECTS. 43 



deny the power of hearing to all insects — a power which, from its 

 great utility for protective purposes, one would expect to find even 

 low down in the scale of living creatures, and which would be 

 rapidly developed by natural selection, whenever any variation in 

 that direction might afford it a basis to work on. Even when for 

 a moment he does grudgingly allow that perhaps some insects 

 may possess this faculty, he hastens to assure us that it is *' most 

 rudimentary," and '* serves no purpose as a warning and protec- 

 tion." Now to my mind the existence of rudimentary hearing 

 faculties, which are entirely useless, is an anomaly calling for an 

 immediate explanation, with which Mr. Arkle does not seem 

 prepared to favour us; though I must remark that their in- 

 utility is a purely arbitrary assumption. The occurrence of 

 such rudiments, if rudiments they be, can only be accounted 

 for in two ways, viz.: — (a) that they are the result of atrophy 

 or degeneration — this explanation would point either to a whole- 

 sale degradation of insects which is not borne out by the facts, 

 or to the assumption that a more specialised form of auditory 

 apparatus exists or has existed even lower in the scale of nature, 

 which I presume the writer would not be prepared to admit; 

 (6) that they are the result of improvement and development, 

 being the earlier links in that long chain which culminates in 

 the complicated ear of the higher vertebrates, and in that case it 

 IS evident that they must come within the scope of, or rather owe 

 their very existence to, natural selection. This appears to me 

 to be the true explanation. But one of the first principles of 

 that far-reaching law is that it can develop only such characters 

 as are actually useful. But Mr. Arkle asserts that these rudi- 

 ments are absolutely useless, which is absurd, as our friend 

 Euclid remarks. I certainly cannot see why anyone should jump 

 to the conclusion that any hearing powers which insects may 

 possess must necessarily be far inferior to those of man, for in 

 the case of two senses at all events they have a decided advantage 

 over us. The human nose would be quite incapable of such feats 

 as are daily performed by coprophilous beetles or the males of 

 ** assembling" moths, and the tactile powers in the body of a 

 caterpillar or the antennae of many insects are far more sensitive 

 and delicate than anything we possess. 



I have lately had good opportunities of observing the habits 

 of a family of insects which numbers among its ranks some of the 

 greatest noise-producers of the whole class ; I mean the Cicadas. 

 I have so far found some nine species of these curious and 

 interesting Homopterans in this immediate neighbourhood, and 

 every day as soon as the sun gets hot the bush resounds far and 

 wide with their ear-splitting sounds, which are certainly more 

 vigorous than pleasing. Now, as is well known, these vocal powers, 

 if I may call them so, are confined to the males, which of itself is 

 a highly significant fact, and, apart from all other considerations, 



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