408 EXTERNAL ANATOMY OF INSECTS. 



The third segment is the mesothorax: it is that prominent 

 part in hep'idoptera, Diptera, and Hymenoptera, through 

 which the entomologist usually passes the pin in specimens 

 for his cabinet ; it bears the fore-wings, and varies in develop- 

 ment in accordance with the functions of those organs. In 

 hepidoptera, the fore-wings are large and powerful, and are 

 the principal organs of flight; consequently, the mesothorax 

 is robust, and in fact the most conspicuous segment of the 

 thirteen. The protliorax, as we have seen, is small and un- 

 important, ruled by the mathematical law, that out of a given 

 quantity of matter divided into portions, if one portion have 

 more than its share, another must have less ; and in insects, 

 the increased segment or segments invariably diminish those 

 immediately adjoining. In Diptera the fore-wings are the 

 only organs of flight, the development of the muscles by which 

 they are moved, and the space required for them, must conse- 

 quently be great ; accordingly we find the mesothorax at its 

 maximum, and the jj^o- and metathorax at their minimum. 

 In Hymenoptera, the hind-wing again becomes an organ of 

 flight; consequently the equilibrium of parts begins to be 

 restored, the prothorax reappears, and the mesothorax de- 

 creases in magnitude ; it is still, however, the principal seg- 

 ment : as we approach the Coleoptera, the genera Cephas 

 and Sirex present a smaller mesothorax, but as I have already 

 pointed out, a larger y;ro^/io/-a.r. In Coleoptera, the fore- 

 wings are not organs of flight, but merely osseous plates or 

 shields to protect the organs of flight, which are the hind- 

 wings only ; accordingly its volume is very much reduced ; its 



this, and at the same time to gain a much more thorough knowledge of the sub- 

 ject than definitions or drawings can possibly give, let me recommend the 

 inquirer to obtain some of the larger species of the principal orders in each class ; 

 for instance, Papilio, Sphinx, Tipula, Tabanus, Bomhus, Tenthredo, Spliex, Ich- 

 neumon, Meloe, Buprestis, Scarahceus, Silpha, Forficula, Gryllus, Acridium, Pentatoma, 

 Notonecta, Cicada, &c., and having thoroughly relaxed them by steeping in hot 

 water, and afterwards dried them on blotting-paper, proceed to the task of care- 

 fully dividing each of them as far as practicable into their thirteen elementary 

 parts ; nature will point out the divisions, but it may require a little care to 

 adhere closely to her guidings. The genus and class of each insect should be 

 written down, and any observation that may occur noted at the time. The 

 learned may smile at the idea of a beginner, like myself, attempting to instruct or 

 offer advice on such points as these ; let him however recollect that advice 

 of this kind may be acceptable to some, and on the score of its possible utility, 

 however limited, let him pardon the writer his presumption. 



