OF PARASITIC ANIMALS. 541 



or less time, and cause different affections: such are, among 

 others, leeches Hirudo medicinalis, and H. alpina; such is 

 probably also the hair-worm, Gordius, It has been thought 

 that the earth-worm could penetrate into the body, it is the 

 effect either of a mistake or of deception. The Furia Inferna- 

 lis of Linnaeus appears to be an imaginary worm. 



Some insects, finally, only mechanically wound the exte- 

 rior surface of the body, or deposit a venom in it; they are 

 otherwise entirely foreign to it. 



THE END. 



