294 
COMPARATIVE ZOOLOGY. 
imago, state, lives from a few hours to several years, and 
dies after the process of reproduction. Growth takes 
place only during larval life, and all metamorphoses occur 
then. Among the social tribes, as Bees and Ants, the 
majority (called “ workers’’) do not develop either sex. 
Insects (the six-footed Arthropods) comprise nearly one 
half of the whole Animal Kingdom, or from one hundred 
and seventy thousand to two hundred thousand species. 
They may be grouped into seven principal orders: 
Lower series: body usually flattened; prothorax large and ) Neuroptera, 
squarish; mouth-parts usually adapted for biting; met- | Orthoptera, 
amorphosis often incomplete ; pupa often active; larva I Hemiptera , 
flattened, often resembling the adult. J Coleoptera. 
Higher series: body usually cylindrical; prothorax small 'A ^ )tera 
mouth-parts more generally formed for sucking; meta- ddoptera 
morphosis complete; pupa inactive ; larva usually cylin- I ’ 
drical, very unlike the adult. J 
1. Neuroptera have a comparatively long, slender body, 
Fig. 263.—Dragon-fly ( Libellula ). 
and four large, transparent wings, nearly equal in size, 
membranous and lace-like. Such are the brilliant Dragon- 
