THE YOUNG NATURALIST. 87 



of the nervures. This is shown at B in the same diagram, and is best 

 seen when a bubble of air is enclosed between the walls of the tube, 

 in a specimen treated as before mentioned. They consist of rings, 

 many of which are incomplete, of horny integument, alternated with 

 similar bands of a thinner substance. These form tubular walls of 

 varying thicknesses, not so much proportioned to the size of the 

 insect as to the greater or less use made by it of the wings with which 

 it is furnished. It is stated that the circulation of the blood may be 

 seen in the wing nervures of some bees, butterflies, and neuroptera, 

 while in the pupal state, but I have not yet had an opportunity of 

 indulging my curiosity in this respect. 



Though the wing membrane is double, with 

 adhesion along the margin and the nervures, it 

 must not be surmised that these are the only 

 points of absolute contact. With careful micro- 

 scopical adjustment the surface of the mem- 

 brane is seen to be divided into minute poly- 

 gonal areolae, to which appearance, and from 

 the six-sided nature of these cells, the term 

 Fig. 2. hexagonal anolation has been appropriately given. 



Fig. 2 represents a very small portion of the upper wing of Acheta 

 domestica (the House Cricket), but it must not be imagined for one 

 moment that the appearance is anything like so strongly marked in 

 the natural membrane, and it is only with lenses of clear definition 

 that it can be seen at all. The resemblance to the facetted eyes of 

 most hexapods is very strong. It is most probably caused by the 

 adherence of the two membranes along the lines of demarcation. 



The primary use of the nervures is undoubtedly to strengthen the 

 wings and prevent them from tearing, for we observe that insects 

 habitually accustomed to remain on the wing for a considerable length 

 of time, possess strong nervures, combined with an extensive supply, 

 their membranes being divided into a large number of cells by them. 



This division of the wing into enclosed spaces, or cells, as they are 

 more correctly termed, by the nervures, is of considerable assistance 

 in the determination of species, especially among insects resembling 

 one another in their characteristics. The nervures also serve another 

 important purpose, being the means of attachment to the body of the 

 insect. Their bases are thickened or expanded, the movements of 

 the wings being anchored to them at this point. 



Some species are remarkable for the almost entire absence of 

 nervures ; more especially is this found to be the case among many 



