Objects for the Microscope. 87 



The wing itself may be described as a transparent mem- 

 branous organ, consisting of two laminae, or plates, which 

 are united by canals called veins or nerves. These veins 

 are hollow channels through which the circulating fluid 

 flows, and a tracheal vessel runs in communication with the 

 tracheae in the thorax. 



In the Ladybird's (Coccinella) wing, the blood is not con- 

 fined to these canals or veins, but circulates freely through a 

 large part of the wing. The circulation may be seen in the 

 wing of any newly-hatched fly, but especially in that of the 

 beautiful lace-winged fly, Hemerobius, where it was first 

 noticed by Dr. Bowerbank. 



WING OF SCATOPHAGA. 



Although this is fully described for the slide of Scato- 

 phaga, mounted whole, it is mentioned here as the best 

 lesson on the veins, and very easily put up separately. If 

 merely mounted dry, the veins are sufficiently seen, but when 

 soaked for a few days in turpentine and mounted in balsam, 

 they become transparent from the expulsion of the air ; and 

 then not only the canals, but the tracheae, may be visible, 

 especially in the costal vein. 



Observe that strong vein bordered with hairs on the 

 fore-margin of the wing that is the Costal vein ; and in 

 the Coleoptera there is inside a little bag of fluid called 

 the Phialum, by which the fly can, at its pleasure, increase 

 the weight of its wing, and sink or fly slowly. 



The short vein next to the Costal, ending at about one- 

 third of the length of the wing, is called the Sub-Costal. 



The next to that is the Mediastinal. 



The next is the Radial, which forks off at its base ; and 

 the farthest branch is the Cubital, always an important vein. 



After the Cubital comes the Prcebrachial, joined to it by a 

 transverse vein, called the Discal transverse. 



WING OF HOUSE-FLY. 

 (Musca.) 



This is an example of the true fly's wing. The Muscidae 

 are very numerous, and divided into many groups and 



