Chai>. xiv. Classification. 367 



Numerous instances could be given of characters derived from 

 parts which must be considered of very trifling physiological import- 

 ance but which are universally admitted as highly serviceable in 

 the definition of whole groups. For instance, whether or not there 

 is an open passage from the nostrils to the mouth, the only charac- 

 ter according to Owen, which absolutely distinguishes fishes and 

 reptiles — the inflection of the angle of the lower jaw in Marsupials 



the manner in which the wings of insects are folded — mere 



colour in certain Algse — mere pubescence on parts of the flower in 

 masses — the nature of the dermal covering, as hair or feathers, 

 in the Vertebrata. If the Ornithorhynchus had been covered with 

 feathers instead of hair, this external and trifling character would 

 have been considered by naturalists as an important aid in deter- 

 mining the degree of affinity of this strange creature to birds. 



The importance, for classification, of trifling characters, mainly 

 depends on their being correlated with many other characters of 

 more or less importance. The value indeed of an aggregate of 

 characters is very evident in natural history. Hence, as has often 

 been remarked, a species may depart from its allies in several 

 characters, both of high physiological importance, and of almost 

 universal prevalence, and yet leave us in no doubt where it should 

 be ranked. Hence, also, it has been found that a classification 

 founded on any single character, however important that may be, 

 has always failed; for no part of the organisation is invariably 

 constant. The importance of an aggregate of characters, even when 

 none are important, alone explains the aphorism enunciated by 

 Linnaeus, namely, that the characters do not give the genus, but 

 the genus gives the characters; for this seems founded on the 

 appreciation of many trifling points of resemblance, too slight to be 

 defined. Certain plants, belonging to the Malpighiaceas, bear 

 perfect and degraded flowers ; in the latter, as A. de Jussieu has 

 remarked, "the greater number of the characters proper to the 

 species, to the genus, to the family, to the class, disappear, and thus 

 laugh at our classification." When Aspicarpa produced in France, 

 during several years, only these degraded flowers, departing so 

 wonderfully in a number of the most important points of structure 

 from the proper type of the order, yet M. Eichard sagaciously saw, 

 as Jussieu observes, that this genus should still be retained amongst 

 the Malpighiacege. This case well illustrates the spirit of our 

 classifications. 



Practically, when naturalists are at work, they do not trouble 

 themselves about the physiological value of the characters which 

 they use in defining a group or in allocating any particular species. 



