142 



THE YOUNG NATURALIST. 



[July 



cover to the underside of the nervure, but is seated upon the upper- 

 side of the corresponding nerve of the right tegminus, which underlies 



the left when laid at rest. By observation, 

 it will be found that the two nervures are 

 then superimposed, and a rapid combination 

 movement of the wing covers, produced by a 

 lateral to and fro vibration, has the effect of 

 rasping the one set of ridges over the other, 

 thus producing a shrill whistle. It is only 

 natural to expect that the resultant sound 

 Fig, 16. will be weak and almost inaudible, but the 



intensity is increased by the communication of the vibrating waves 

 to the surrounding membrane, which is admirably adapted to receive 

 and magnify such impressions. The large cells into which a great 

 portion of the wing covers is divided, will all unite their individual 

 vibration to swell the volume of the sound. 



(To be continued.) 



Notes on the uncertain abundance of many 

 Lepidoptera. 



By W. H. TUGWELL. 



In considering this most interesting subject, it is convenient to 

 divide the species referred to into two classes. The first comprises 

 the bulk of our truly indigenous Lepidoptera, which, although found 

 every year in their respective haunts, yet from causes which are 

 apparent to most observers, naturally vary in numbers from year to 

 year. Each and every species have their many enemies which prey 

 upon them, from the egg to the perfect state ; it is little to be 

 wondered that they should appear in greater or lesser numbers 

 according to the coincident presence or absence of their many foes. 

 What with birds, mice, coleoptera, ichneumons, ants, diptera, spiders, 

 with unpropitious weather, &c, the marvel is that so many do reach 

 maturity, and are able to carry on their race. 



Very much could be written on this subject, but I purpose rather 

 to treat on my second class, viz., those rare visitants that from time 

 to time reach our shores. There are many lepidoptera of powerful 

 flight and roving habit whose range is almost world-wide, and altered 

 but little in character under widely different climes ; still, of course, 



