144 BOARD OF AGRICULTURE. 



In the Insects again, there are three modes of disposing the 

 rings, and their appendages : 



1. Where the number of segments is indefinite, and much like 

 each other in form, supporting both thoracic and abdominal legs ; 

 as in the order of 3Iyriapoda. 



2. Where the head and thorax are ^osely united ; and there 

 are eight pairs of legs attached to the thorax alone, as in the 

 Arachnida. 



3. Where there are three distinct regions to the body ; the 

 head, thorax and abdomen, as in the Insecta. Moreover the true 

 insects have three pairs of legs attached to the thorax ; and are 

 winged. 



The Myriapods grow by the addition of rings, after hatching from 

 the egg ; the Arachnids by frequent moultings of the skin ; while 

 the winged insects pass through a distinct metamorphosis. The 

 young insect after being hatched from the egg is called the larva, 

 from the Latin term meaning a mask, since it was the ancient be- 

 lief that it concealed beneath its skin the form of the perfect insect. 

 When full-fed, the pupa-skin rapidly forms beneath the tegument, 

 and the insect in that form escapes through a slit in the back of the 

 larva. The perfect insect is often called the imago. The larval 

 state of insects which resembles worms, has also an analogous 

 form to the Myriapods ; so spiders are analogous to Crustacea, 

 while reminding us of the pupa state of the winged insects. 



Moreover, worms and Crustacea are, generallj'- speaking, aquatic, 

 breathing by gills, while insects are terrestrial and breathe by 

 pores in the side of the body which communicates with a complex 

 system of air tubes, including tubular blood vessels. 



The order of winged-insects is subdivided into seven divisions, 

 occup3'irig an intermediate rank between orders and families, and 

 called by naturalists suborders. Of these the Symenoj^tera seem 

 to be highest in the scale, and the Neuroptera the lowest. 



Before characterizing these suborders, a few explanations will be 

 necessary to understand the terms applied to the different parts. 

 In insects as in the higher animals, the parts are repeated on either 

 side of the middle of the body, with the exception of the single 

 intestinal canal, and the dorsal vessel, which performs the func- 

 tions of a heart. 



In this head of a bee here figured we have all the parts connected 

 with the function of sensation, and those adapted for seizing and 



