MICROSCOPIC DRAWING AND ENGRAVING. 



In due time, generally towards the decline of summer, the young, 

 breaking the shell, issues from the egg in the form proper to the 

 . 9 g first of the ^hree 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 ono 

 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 tracheaB, 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 



