MICROSCOPIC DRAWING AND ENGRAVING. 
Firr 28. 
In due time, generally towards the decline of summer, the young, 
breaking the shell, issues from the egg in the form proper to the 
first of the three stages of its existence, in which it 
is called a larva ; its length, when full grown, in this 
state, is about half an inch, and it is represented in 
its proper magnitude in fig. 28. It is represented 
magnified in its linear dimensions 6| times; and, 
therefore, in its superficial dimensions, 42 times, in 
fig. 29.* 
38. As the larva increases in size, the serpentine 
vessels attached to its sides become more apparent, and 
the tail assumes that rich feathered appearance which, in con¬ 
junction with the paddles projecting from its sides, constitute one 
of its most beautiful features. 
The body of the insect when young, being very pellucid, its inter¬ 
nal organisation may be very clearly seen with the microscope by 
light transmitted through it. The peristaltic motion of the intestines; 
the circulation of blood, and the pulsations of the dorsal vessel, 
which in these creatures supplies the place of a heart, can be 
observed with the greatest facility. As it grows, it assumes a 
variety of colours, losing much of its transparency, when it is a 
few months old ; at which time, the period approaches at which it 
is destined to pass into the second stage of its existence. The 
eyes, as will be seen in the figure, are large, protuberant, and 
curiously reticulated; they are of a citron colour. The body 
exhibits a beautiful play of various tints, finally assuming a rich 
brown colour, with various shadings. 
39. It must be here observed, that the important function of 
respiration is performed in a very different manner, by different 
animals ; the breathing apparatus being always admirably adapted 
to the element which they inhabit. The higher class of animals 
respire through the mouth and nose. Fishes take air through 
their gills, and insects through orifices provided for the purpose, 
either in the hinder extremity of their bodies, or along their sides. 
From these openings, the air passes through, and inflates vessels 
called tracheae, which extend along their sides; in these it en¬ 
counters the blood, on which it produces effects similar to those 
produced in the superior animals. These vessels appear in the 
figure running along each side of the body, and throwing out 
numerous ramifications which traverse the several leaf-shaped 
paddles projecting from the body. 
The orifices by which air is supplied to the tracheae for respira- 
* This figure and the succeeding ones, drawn by Dr. Goring, have been 
copied with the permission of Mr. Pritchard from the microscopic 
illustrations. 
76 
