154 THE NORTHERN MICROSCOPIST. 
the two hollows show the insertion of the coxe. Then there is the 
meso-thorax and upper portion of the abdomen, and the metaster- 
num and abdomen (under surface), on the margin of which we 
notice the favapleura or side pieces, while in front we find the 
episterna or breast pieces. As the wings are above the abdomen, 
we may notice the appearance of the wing when folded and when 
extended. 
We may now notice the scwtel/um or shield. You will remember 
that I termed the projection in front of the head the clypeus or 
shield. Both terms are borrowed from the Latin. The cdypeus 
was a small circular shield used by the Roman foot soldiers, 
while the “scutum” was a larger shield and of a different 
shape, used by cavalry as well as infantry. The chief objects of 
interest here are the e/ytra, or wing cases. The point nearest to 
the scutellum is called the base, while the pointed end is known as 
the apex. The e/y¢von forms (as I mentioned before) a pleasing 
object when viewed by means of polarized light. The parts of the 
intermediate and posterior pair of legs are similar to the anterior 
pair; but in the water beetles they assume the form of swimming 
paddles—being flattened, the margins being thickly set with hairs 
which contain air, and besides rendering the body lighter afford a 
store for respiration. The next point to notice is the folding process 
of the wings, by means of which arrangement they are safely 
stowed away in small compass when not required. The eye of the 
beetle is well worthy of notice, being compound and composed of 
a large number of facets; but, although these facets give a great 
advantage to the beetle in seeing all around, yet it must be 
remembered that only one image is conveyed to the brain. The 
thorax bears all the instruments of locomotion, both legs and wings, 
and these work in strong processes which give them needful 
support,—the power of motion being derived from sets of powerful 
muscles wonderfully adapted for their work. 
As we find rapacious animals inhabiting the earth, and carniv- 
orous creatures inhabiting the sea, so we find a similar division 
of the beetle family ; carnivorous beetles living on land, and 
others with similar tastes inhabiting the water; or, as our great 
poet expressed a similar idea :—‘‘ There be land rats and water 
rats, water thieves and land thieves ;” and as the Dytiscus happens 
to ply his daily avocation in the water, he belongs to that class 
of beetles known as the ‘“ Hydradephaga” or carnivorous beetles 
of the water. The word Hydradephaga is derived from two Greek 
words, meaning water-eater. We notice in the animal world 
generally, that natural provision is made in various ways to enable 
creatures to obtain food according to the circumstances in which 
they are placed ; and innumerable modifications of limbs and other 
parts of the body take place, in order to fit them more suitably 
