7 
ANATOMY AND PHYSIOLOGY. 91 
strictly speaking, be called the prosternum. It carries 
the front pair of legs, which are the only appendages 
of this division of the thorax. 
We must sacrifice many specimens to gain any 
clear idea of the arrangement of these parts. The 
lines of division between the different segments are 
more easily traced on the inner than on the outer 
surface, and in a dried than in a recent specimen. 
If we break a dried thorax carefully to pieces, we 
find the edges turned in to fit against each other 
along these lmes of division. The first and last 
rings of each segment, in fact the pree-scutum and 
the post-scutellum, are, as a rule, thus turned in and 
do not appear at all on the surface. By the appo- 
sition of these flanges the connection is strengthened, 
and a ridge is formed for the attachment of muscles 
on the inner surface. 
The meso-thorax is chiefly represented by its 
scutum or second, as the pro-thorax is by its scu- 
tellum or third, component rng. The peculiar 
conformation of the back of the thorax of wasps is 
due to the development of the meso-scutum into a 
broad convex surface. It is black in the smaller 
wasps but variegated in the hornet. Behind it lies 
the scutellum, which is a trarisverse band, brown in 
the hornet, but in the wasps black, with the exception 
of a semicircular yellow spot at each end. — 
Not to map out the thorax with tedious minute- 
ness, I would only indicate the chief divisions on its 
lateral aspect. As the divisions of the back are 
expressed by variations of the word scutum, so the 
sides have had the word sternum appropriated to 
them in nearly the same way: there is a pro-, meso-, 
