MAY-FLIES AND THEIR NEIGHBOURS 209 



span is brief, maybe but an hour, or even less 

 according to some authorities. Reaumur con- 

 sidered that individuals living from the evening 

 of their emergence until the sunrise of the next 

 day would be Methuselahs in a tribe of which 

 the greater number never see the light of the sun 

 at all. Although Nature provides these insects 

 with wings but for "the sport of an hour," it does 

 not follow by any means that she slights her 

 work on that account. I have shown in 

 Fig. 139 a portion of one of the wings of a 

 May-fly considerably magnified, to exhibit its 

 beautiful veinwork and structure. With the eyes 

 of the May-fly, too, Nature has taken infinite 

 pains in some species for there are about forty 

 species in Great Britain enriching them with 

 seven eyes of three kinds. Two of these are 

 compound pillared eyes and are raised above the 

 head ; then there are the two ordinary compound 

 eyes of insects, which are generally on either side 

 of the head, while between these and in front of 

 the head there are three ocelli or single eyes. 



Another interesting point in the anatomy of 

 the May-fly is its mouth. As it neither requires 

 nor has time in its winged state to eat or drink, 

 its mouth organs become atrophied, leaving 

 nothing but a small air passage which leads 

 to the alimentary canal. The latter, however, 



