150 THE NORTHERN MICROSCOPIST. 
and apparently he is a formidable check to over population, for 
where he is to be found in large numbers, fish and newts have a 
lively time, for he seems to delight in a war of extermination so far 
as his inferiors are concerned. Before proceeding to examine the 
beetle in question it will be necessary for a thorough comprehension 
Fig. 23. 
of the subject to glance at the leading features of insects, in which 
class the beetle family holds the first rank. 
Insects may be described as articulated animals, breathing by 
means of trachez, and divided into three distinct portions, viz., the 
head, the thorax, and the abdomen; passing through a series of 
- transformations, and having in the perfect or winged state six artic- 
ulated legs and two antennz. ‘The bodies of insects are formed 
of a series of rings, within which are contained the muscles and 
vital apparatus. 
As I have just stated, insects are articulated animals, breathing 
by means of trachez. Now, the trachez are tubes composed of two 
thin membranes, kept open by a fine but stiff wirey thread, which is 
twisted spirally between the two coats throughout the whole course 
of the tube. This arrangement keeps the tube open, however 
much it may be twisted or bent. The breathing apparatus is not 
specially consigned to any portion of the insect as is the case with 
the lungs in man or the gills in fish, but it permeates the whole 
structure of the insect, passing through the limbs, and even reach- 
ing to the claws. The trachea, fig. 24, will illustrate this spiral 
thread, which in its convolution is so curved as to give the appear- 
ance of watered silk. It is the main portion of the trachea, 
consisting of a cylindrical tube, with smaller tapering tubes leading 
