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PREFACE TO THE THIRD EDITION. 



SEVERAL important changes, and many slight altera- 

 tions, have been made in this edition. The author would 

 especially call attention to the change in his views as to 

 the number of segments in the head of hexapodous in- 

 sects ; there being four instead of seven (see p. 19). On 

 p. 52 will be found a notice of parthenogenesis in the 

 pupa of Chironomus, and on p. Ill an account of the 

 recently discovered glands for secreting wax ; while on 

 p. 258 correct figures of the larva and pupa of Melitcea 

 Harrisii are given, and a brief account of the Linguatulina 

 is added. It is hoped that these changes, with the ad- 

 dition of four more plates, and an appendix, will bring 

 the work up to the present state of the science. 



The author should here state, in justice to himself, that 

 the primary object in preparing the systematic portion of 

 the work was to give as clear a view as possible of the 

 larger groups of insects ; so that the groupings of the 

 families into subdivisions of suborders has been omitted 

 for the sake of perspicuity. Thus, the difference between 

 the Heteropterous and Hemipterous divisions of the 

 Hemiptera is not perhaps so clearly indicated as may 

 seem desirable ; so also, the difference of the Tenthre- 

 dinidas and Uroceridse from the rest of the Hymenoptera, 

 of the Lice from the rest of the Hemiptera, or the Lepis- 

 matidtie, Campodese and Poduridse, from the remainder of 

 the Neuroptera. Perhaps in endeavoring to bring out 

 clearly the essential unity of organization in the members 



