CHAPTER VIII. 



CLASS IV. INSECTA.* 



Arthropods having in the adult condition three pair of 

 legs, usually two pair of wings and the body divided into three 

 regions, (i) the head which bears a single pair of antennae and 

 certain mouth parts, (ii) the thorax and (iii) the abdomen. Respira- 

 tion tracheal. Young always more or less different from the 

 adult and complete metamorphosis very frequent. 



Insects are segmented animals and as in the Crustacea and the 

 Arachnida the segments are grouped into higher categories. 

 Three regions, or tagmata as Lankester calls them, the head, the 

 thorax and the abdomen are present. The thorax always has 

 three segments, but the number in the head and in the abdomen 

 of an Insect body is still a disputed point. The two most domi- 

 nant views are those of Heymons f and of Lankester, { the latter 

 of whom founds his enumerations on the researches of Folsom. 

 The discrepancy between these two views, which are fully dis- 

 cussed on pp. 318 ff., is readily seen from the following table : 



* D. Sharp, The Cambridge Natural History, Insects, London, vol. i, 

 1895, vol. ii, 1899. Berlese, Gli Insetti, now in course of publication, 

 Milano. Packard^ Textbook of Entomology, New York and London, 1898. 

 Miall and Denny, The Cockroach, 1886. Henneguy, Les Insectes. Lowne, 

 Anatomy of the Blow-fly. Lyonnet, Traite anatomique de la Chenille qui 

 range le bois de Saule, The Hague, 1762. J. Lubbock, On the Senses, 

 Instincts and Intelligence of Animals with special reference to Insects, Int. 

 Sci. Ser., Ixv, 1888, and Tr. Linn. Soc. London, xxiii, 1860. Newport, 

 Phil. Trans., 1837, p. 259. Kirby arid Spence, Introduction to Entomology, 

 London, v. Ed., 1828. L. O. Howard, The Insect Book, New York, 1901. 



t Die Segmentirung des Insectenkorpers, Abh. Ak. Berlin, 1895. 



% Article Arthropoda, Encycl. Brit., 10th Ed., vol. xxv. 



The Development of the Mouth Parts of Anurida maritima Guer, 

 Bull. Mus. Harvard, xxxvi, 1900. 



608 



