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VARIOUS INSECT STRUCTURES. 



By Edward M. Nelson, F.R.M.S. 



{Read May 25th, 1915.) 



The wing of Agrion pulchellum (Neuroptera) is not only a wonder- 

 ful, but a particularly interesting microscopical object. The 

 membrane, which in life reflects beautiful colours, is double, 

 each part being bordered by a stout rim edged with formidable 

 saw-like teeth. The surface of the wing is divided into com- 

 partments by nervures which are peculiar ; for the transverse 

 bars, as well as four of the longitudinal bars, have on one edge 

 thorns just like those on a sloe-bush, and on the other edge 

 saw-like teeth ; there are three other longitudinal ribs, which 

 have saw-like teeth on one edge and very fine teeth on the other, 

 but no thorns. 



This beautiful microscopical object forms an excellent test for 

 low powers, " loups " or simple microscopes. 



At one part on the edge of the wing there is a dark-coloured 

 compartment, inappropriately called the " stigma." This really 

 is a pocket, the two membranes being separated from one another 

 at this point by some brown cellular tissue, the saw-edged 

 borders of the membranes being kept apart, thus forming an 

 opening. Obviously, then, the " stigma ' is an apparatus for 

 producing a sound, much in the same way as the " bull roarer " 

 of our childhood. The " stigma ' can be seen readily by the 

 naked eye, as it measures 1*1 mm. x 0'5 mm. 



If we replace the low power by a 1/2 inch, a careful examina- 

 tion of the border of the wing reveals a delicate hair between 

 the teeth of the saw (fig. 1). 



These hairs are minute, the largest one found measured only 

 23 fx in length and 2 fx in breadth ; but on other species of Dragon- 

 flies they are larger and more easy to demonstrate. These hairs 

 spring out of circular rings, after the manner of most hairs on 

 insects, and not like the small ones on the membrane of the 

 blow-fly's tongue, which have no rings. While on this subject of 



Journ. Q. M. C, Series II. No. 77. 33 



