CHAP. XV 



Backboneless Animals 



241 



appearance, with a soft and beautiful skin, with unjointed legs, with 

 the halves of the ventral nerve-cord far apart, and with many other 

 remarkable features, it has for us this special interest that it 

 possesses the air- tubes characteristic of insects and also little 

 kidney-tubes similar to those of Annelids. 



(c) Myriapoda. — Centipedes and Millipedes.— These animals 

 have very uniform bodies, there is little division of labour among the 

 numerous appendages. The head is distinct, and bears besides the 

 pair of antennas (which Peripatus and Insects also have) two pairs 

 of jaws. The Centipedes are flattened, carnivorous, and poisonous ; 

 the Millipedes are cylindrical, vegetarian, and innocuous ; moreover,' 

 they have two pairs of legs to most of their segments. 



Fig. 47. — Winged male and wingless female of Pneumora, a kind of 

 grasshopper. (From Darwin.) 



(d) Insecta. — Insects are the birds of the backboneless series. 

 Like birds they are on an average active, most have the power of 

 flight, many are gaily coloured, sense-organs and brains are often 

 highly developed. 



Contrasted with Peripatus and Myriapods, they have a more 

 compact body, with fewer but more efficient limbs. They are 

 Arthropods, which are usually winged in adult life, breathe air 

 by means of tracheae, and have frequently a metamorphosis in their 

 life-history. To this definition must be added the anatomical facts ■ 

 that the adult body is divided into three regions, ( I ) a head with 

 three pairs of mouth -appendages ( = legs) and a pair of sensitive 

 outgrowths (antennae or feelers) in front of the mouth, (2) a thorax 

 with three pairs of walking legs, and usually two pairs of wings, 

 and (3) an abdomen without appendages, unless occasional stings; 

 egg-laying organs, etc., be remnants of these. 



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