ANATOMY AND PHYSIOLOGY. 93 
band, narrowed to a point at either end, and drawn 
out in the middle into a cusp, which nearly divides 
the scutellum behind it into two. This cusp marks 
externally the position of a longitudinal ridge which 
affords attachment to the great depressor muscles 
of the wings within. The scutellum again has a 
peculiar form, something like that of that most useful 
object of comparison, the ace of hearts. There is 
not much of this portion of the meta-thorax to be 
seen on the back, but on either side a broad round 
surface appears, on which the orifice of the second 
thoracic spiracle is a conspicuous object. This ar- 
rangement is characteristic of the Hymenoptera. In 
all other orders of insects the second pair of thoracic 
spiracles are placed, like the first, in the division 
between two segments, between the meso- and 
meta-thorax ; in the Hymenoptera they are formed 
in the meta-thorax itself. The post-scutellum, in the 
form of a narrow ring notched for the passage of the 
tendon of the suspensory muscle of the abdomen, 
closes the thorax behind. 
The meta-sternum, as the whole thorax narrows, 
is smaller than the meso-sternum, but, like it, slopes 
off behind to a point which bears the hind legs. 
The hind wings are attached over its upper ex- 
tremity.* 
The study of the skeleton is only the opening of 
* The article Insecta, in the Natural History division of the 
‘English Cyclopedia,’ may be consulted with advantage on the subject 
of the Anatomy of Insects, by those who have not the opportunity or 
the leisure to study the more elaborate essay in the ‘ Cyclopedia of 
Anatomy and Physiology.’ The diagrams of the thorax of the hornet 
are beautifully clear. 
