Ivi PRELIMINARY SKETCH OF THE 



Geoffroy has described the organs in which it 

 is produced in the Silurus of the Nile. 



It would be unpardonable to pass over in 

 this brief notice the mention of a work which 

 has contributed so much to the progress of 

 zoological knowledge, as the annals of the 

 Museum of Natural History in Paris, or that of 

 our own Philosophical and Linnaan Transac- 

 tions, to which, however, no praise of ours can 

 give an additional lustre. 



We now conclude this historical sketch of 

 the progress of the science to proceed to a 

 brief notice of the principal methods, entreat- 

 ing our readers to pardon the imperfections to 

 which the immensity of the subject, the slen- 

 derness of our abilities, and the narrowness of 

 our limits, have necessarily exposed us. 



It is obvious on the slightest view of the 

 subject, that the immense number of various 

 objects embraced by natural history could never 

 be retained in the memory without an arrange- 

 ment of divisions and subdivisions founded upon 

 some distinguishing characteristics sufficiently 

 marked to assist retention. Such divisions and 

 subdivisions have accordingly at all times been 

 used by naturalists, founded on characters of 

 greater or less precision in proportion to the 

 progress of science. Aristotle adopted a sys- 



