STRUCTURE OF INSECTS. 375 



and magnitude of the articulations, by which they are 

 jointed to each other, differ much in the different 

 species. The articulation of the head with the thorax 

 can always be determined, and so can the division of 

 the others, if not by the articulation, at least by the 

 annuli or rings. Whatever may be their dimensions, 

 or the mode in which they are joined together, the first 

 ring behind the head is the thorax, the second the breast, 

 and all the remainder, however many rings there may 

 be, the abdomen. 



The head, as is the case with other animals, contains 

 the mouth and the organs of the senses : the only 

 ones of which the functions or the plan is known with 

 certainty, are the eyes, and the antennae or feelers, which 

 last are conceived to be more particularly organs of touch. 

 The muscles that move the head, take their rise near 

 the abdominal extremity of the trunk, and have their in- 

 sertion within the occipital opening. They are inserted 

 in the direction toward which they move the head, and 

 have their origin at the opposite side of the trunk, so that 

 they cross the trunk inside diagonally ; and they produce 

 their motion by contraction, the same as the muscles of 

 quadrupeds. In most insects the muscles that move 

 the head downwards, are more powerful than those that 

 move it in any other direction. 



The thorax occupies the first ring of the trunk. It is 

 in some species very small ; but generally the centre of 

 the under part of it is formed into a prominent sternum, 

 or keel, and the fore legs are articulated to it one on 

 each side ; and the upper part sometimes terminates 

 backwards in a spine, with which the insect is capable 

 of inflicting a wound. 



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