98 THE ANIMAL KINGDOM. 



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 Prwbrachial, joined to it by 

 a transverse vein, called the Discal transverse. 



WING OF HOUSE-FLY. 



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

 are very numerous, and divided into many groups and fami- 

 lies ; the third joint of the antennae, always the largest in 

 this family, enables us to recognise a true Musca at once. 

 After that we must look at the wing, which varies very much 

 in the number and -position of its veins. 



There are many house-flies. The Musca domestica will 

 show the praebrachial vein, forming a rounded obtuse angle 

 at its flexure, nearly straight from thence to the tip ; the 

 discal transverse vein nearly straight, parted from the border 

 by more than half its length. 



This little wing makes 600 strokes a second, carrying it 

 five yards ; if alarmed, can increase its velocity to thirty -five 

 feet in a second. 



WING OF BLUE-BOTLLE FLY, 

 (Musca romitoria,) 



will show the Discal transverse vein with two distinct 

 curves, parted from the border and from the flexure of the 

 praebrachiai by hardly one third 0f its- length. The an- 

 tennae of this fly have the third joint remarkably long, and 

 furnished with peculiar organs of smell. (See Antennae of 

 Blow-fly.) 



