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9'2 LECTURE IX. 
^Sals^f^thiis we know that a Flea and a Grasse 
hopper are capable of springing to a much greater 
distarice in proportion to the length of their bodies 
than any quadrupeds; for a Flea is capable of 
springing at least 200 times its own length; 
whereas the Jerboa and the Kanguroo, in their 
most powerful springs fall very far short of the 
same proportional distance. 
^ We have before observed that insects are not 
provided with lungs, like the higher orders of ani>- 
mals, but that they breathe by means of a certain 
number of pores or small openings, generally 
placed on each side the body, and which are con- 
tinued into very numerous branches, dispersed 
about the body of the animal. If the lateral 
pores or breathing-holes in insects be stopped, 
by rubbing them with oil or any other sub- 
stance capable of excluding the air, the animal, 
after a certain time, falls into convulsions and 
dies. 
It has been a matter of doubt among natu- 
ralists, and particularly those of the French school, 
whether insects can properly be said to have a 
circulation of the blood; and whether they have 
any organ that can properly be called a heart. 
