CHARTERS 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 
Dynastes 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 c@sar 
of the Philippines, 255 mm.; and the Brazilian noctuid Erebus 
agrippia, 280 mm. Some of the exotic wood-boring larve 
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- 
gidze, some of which are only 0.25 mm. in length, as are also 
certain hymenopterous egg-parasites of the families Chalcid- 
ide and Proctotrypide. 
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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