OR, PL A ITT TEACHING. 



35 



196. 



also hooks, 19, by which they cling- 

 to any roughnesses. By these 

 they become en- 

 tangled in spiders' 

 webs, and are pre- ^ 

 vented from walk- 

 ing upon woolly 

 surfaces. Th eir feet 

 are also covered 

 with hairs, 20, by 

 which they brush 

 and cleanse them- 

 selves. 



The proboscis of butterflies 

 is formed of three tubes, 1; the 

 lateral ones, 2, 3, 

 by their muscular 

 fibres, act upon the 

 central tube, 4, and 

 cause it to convey 

 nectar to the mouth — these in- 

 sects not having the power of 

 exhausting the proboscis and 

 creating suction. The suckers of 

 some insects are provided with 

 lancets, for puncturing the bark 

 and leaves of trees. Some of the 

 Aphides have these punc- 

 turing tubes double the 

 length of their bodies. 

 When moving, the Aphides 

 extend these tubes under- 

 neath their bodies, from 

 which they project, and 

 have the appearance of 

 tails, 6. Fleas are provided with 

 lancets, 7, 7, on each side of their 

 tongues, 8 ; with 

 these they make 

 incisions in animal 

 bodies, and draw 

 blood, upon which 

 they feed. Chica- 

 goes, gnats, mos- 

 quitoes, and other suctorial in- 

 sects, are similarly provided. 



198. 



199. 



Insects breathe through pores 

 distributed along the sides of 

 their bodies, which pores are 

 called stigmata, 

 9, communicat- 

 ing with inter- 

 nal air-vessels, or 

 trachece,10. The 

 air is renewed 

 in the trachea; 

 by the expan- 

 sion and contraction of the ab- 

 domen, 3-181. 

 Insects open 

 their wings by 

 forcing air into 

 the nervures, 12, 

 ^ and close them 

 by expelling it 



therefrom. The 

 blood of insects 

 has motion, but 

 can scarcely be 

 said to circulate. 

 In the centre of 

 their bodies is 

 a large blood- 

 201 - vessel, 11, which 



serves as a heart, and has a pulsa- 

 tory movement. 

 In this there are 

 valves, which al- 

 low the fluids to 

 pass only one 

 way. But as 

 the blood meets 

 every where 

 with air-vessels, 

 9, 10, and is kept 

 in motion by the 

 dorsal vessel, 11, 

 no lungs are re- 

 quired, and 

 there are no 

 veins nor venous 

 202. blood. The blood 



