30 MEMOIR OF 



bears the greatest resemblance, either naturally, 

 or agreeably to the principles of his system ; and 

 having fixed on it, he denominates the variety a 

 species. Thus, the hooded crow is a species of 

 crow. So also, having determined which des- 

 cription of the humming bird he will consider 

 generic, he denominates the varieties and devia- 

 tions from this description within certain limits, 

 as the different species of humming birds. To 

 each of the different species some name is given 

 descriptive of its chief distinctions, and thus, 

 those who agree in the use of the same classifica- 

 tion, and of the same names of the different 

 species, can readily enable each other to find in 

 books any particular species. 



Thus, genera and species are founded in re- 

 semblances ; and by assorting animals together, 

 agreeably to any particular resemblances which 

 may be determined on for the purpose, whether 

 toes, teeth, claws, beaks, habitation, food, habits, 

 &c. a system is formed, and the particular point 

 of resemblance adopted by any individual natu- 

 ralist distinguishes his particular system, and in 

 the superior advantages for scientific purposes of 

 any author's classification, consists the superiority 

 of his system. 



The most obvious resemblances are not, how- 

 ever, always to be chosen for the purposes of 

 system. 



" The rudest wanderer in the fields, " observes 

 an eminent writer,"* may imagine that the pro- 

 * Dr Brown's Philosophy of the Human Mind. 



