178 ESSAY ON CLASSIFICATION 



another, whether living in flocks, small companies, or isolated; 6th, 

 in the period of their reproduction; 7th, in the changes they undergo 

 during their growth and the periodicity of these changes in their 

 metamorphosis; 8th, in their association with other beings, which is 

 more or less close, as it may only lead to a constant association in 

 some, whilst in others it amounts to parasitism; 9th, specific charac- 

 teristics are further exhibited in the size animals attain, in the pro- 

 portions of their parts to one another, in their ornamentation, etc., 

 and all the variations to which they are liable. 



As soon as all the facts bearing upon these different points have 

 been fully ascertained, there can remain no doubt respecting the 

 natural limitation of species; and it is only the insatiable desire of 

 describing new species from insufficient data which has led to the in- 

 troduction in our systems of so many doubtful species, which add 

 nothing to our real knowledge, and only go to swell the nomenclature 

 of animals and plants already so intricate. 



Assuming then that species cannot always be identified at first sight, 

 that it may require a long time and patient investigations to ascertain 

 their natural limits; assuming further that the features alluded to 

 above are among the most prominent characteristics of species, we 

 may say that species are based upon wejl determined relations of in- 

 dividuals to the world around them, to their kindred, and upon the 

 proportions and relations of their parts to one another, as well as 

 upon their ornamentation. Well digested descriptions of species 

 ought, therefore, to be comparative; they ought to assume the char- 

 acter of biographies and attempt to trace the origin and follow the 

 development of a species during its whole existence. Moreover, all 

 the changes which species may undergo in course of time, especially 

 under the fostering care of man, in the state of domesticity and cul- 

 tivation, belong to the history of the species; even the anomalies and 

 diseases to which they are subject belong to their cycle, as well as 

 their natural variations. Among some species variation of color is 

 frequent, others never change, some change periodically, others acci- 

 dentally; some throw off certain ornamental appendages at regular 

 times, the Deers their horns, some Birds the ornamental plumage they 

 wear in the breeding season, etc. All this should be ascertained for 

 each, and no species can be considered as well defined and satisfac- 

 torily characterized the whole history of which is not completed to 



