230 THE COURTSHIP OF ANIMALS 



It is curious that these creatures, which in their winged 

 state have never seen the sun, should be attracted by 

 light. But such is the case. I well remember witnessing 

 an instance of this years ago, while staying, one August, 

 at Bingen on the Rhine. Dinner was served in the open 

 air, and just as the soup was served May-flies in myriads 

 swarmed round the lamps and fell on the tables as thick 

 as snow-flakes. Some of these were in copula, and I 

 succeeded in bottling a few specimens for the British 

 Museum, where they still remain to remind me of this 

 amazing scene. 



About three hundred species of May-flies are known, and 

 some enjoy a somewhat longer span of life than others. 

 In no case, however, do they emerge till just before sunset ; 

 but in some species it is believed life may be prolonged 

 for as much as three or four days, or even longer, if the 

 weather be cold and wet, so as to keep them in a state 

 of enforced rest, which amounts to a state of coma. 



That their hold on life during this final stage of 

 existence is brief there can be no gainsaying, for it is 

 passed fasting. Jaws are wanting, and the whole 

 alimentary canal has been transformed into one long air- 

 chamber. Its walls are now of extreme tenuity, and by 

 changes in the interior of the tube, valves are formed which 

 convert the stomach into a capacious air-sac. " When 

 movements," remarks Dr. David Sharp, " tend to increase 

 the capacity of the body cavity then air enters into the 

 stomachic sac by the mouth orifice, but when muscular 

 contractions result in pressure on the sac they close the 

 orifices of its extremities by the valve-like structures 

 just referred to ; the result is, that as the complex move- 

 ments of the body are made the stomach becomes more 

 and more distended by air." It was known even to the 



