CHAPTER II 



ANATOMY AND PHYSIOLOGY 



i. SKELETON 



Number and Size of Insects. The number of insect spe- 

 cies already known is about 300,000 and it is safe to estimate 

 the total number of existing species as at least one million. 



Among the largest living species are the Venezuelan beetle 

 Dynast es hercules, which is 155 mm. long, and the Venezuelan 

 grasshopper Acridium latreillei, which has a length of 166 

 mm. and an alar expanse of 240 mm. Among Lepidoptera, 

 Attacus atlas of Indo-China spreads 240 mm.; Attacus casar 

 of the Philippines, 255 mm. ; and the Brazilian noctuid Erebus 

 agrippina, 280 mm. Some of the exotic wood-bpring larvae 

 attain a length of 150 mm. 



The giants among insects have been found in the Carbonif- 

 erous, from which Brongniart described a phasmid (Titano- 

 phasma) as being one fourth of a meter long. 



At the other extreme are beetles of the family Trichoptery- 

 gidse, some of which are only 0.25 mm. in length, as are also 

 certain hymenopterous egg-parasites of the families Chalcid- 

 idse and Proctotrypidae. 



Thus, as regards size, insects occupy an intermediate place 

 among animals; though some insects are smaller than the 

 largest protozoans and others are larger than the smallest 

 vertebrates. 



Segmentation. One of the fundamental characteristics of 

 arthropods is their linear segmentation. The subject of the 

 origin of this segmentation is far from simple, as it involves 

 some of the most difficult questions of heredity and variation. 

 As arthropod segmentation is usually regarded as an inher- 

 itance from annelid-like ancestors, the subject resolves itself 



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