ENTOMOLOGY. 243 



structed as to enable it to form a number of small 

 concavities, which act like so many cupping-glasses 

 or a boy's sucker, and the atmospheric pressure re- 

 tains him in his position. 



The foot of the common fly also is capable of 

 forming the same concave vacuities, which enable it 

 to proceed against the laws of gravity. 



Poisonous Serpents. 



Of forty-three kinds of serpents examined by Dr. 

 Russel, only seven were found furnished with poison- 

 ous organs. 



The Leech. 



There is no outlet to the intestinal canal disco- 

 vered in the common leech ; mere transpiration is all 

 that it performs, the matter oozing through, and fix- 

 ing on the surface of the body, whence it afterwards 

 separates in small threads. 



If it be intended that the leech shall draw a large 

 quantity of blood, the end of the tail is cut off, and it 

 then sucks continually. 



Leeches may be frozen stiff like pieces of ice, and 

 easily re-animated, for a leech has no heart. 



Three Hearts. 



The poulpe, the seiche, and the calmar genera of 

 the mollusca tribe, are provided with three hearts* 



Shells. . 



The matter of tbe shell is secreted by the corium 

 or skin of the insect, and the form it assumes is re- 

 gulated by the body of the animal. It is coeval with 

 its existence, and appears previous to the exclusion 

 of the egg. The solid matter of the shell consists of 

 common lime united with a small portion of animal 

 matter resembling coagulated albumen. The mouth 



