CHAP. XIV.] CLASSIFICATION. 345 



structure from the proper type of the order, yet M. Richard 

 sagaciously saw, as Jussiou observes, that this genus should still 

 be retained amongst the Malpighiaceae. 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. 

 If they find a character nearly uniform, and common to a great 

 number of forms, and not common to others, they use it as one of 

 high value ; if common to some lesser number, they use it as of 

 subordinate value. This principle has been broadly confessed by 

 some naturalists to be the true one ; and by none more clearly 

 than by that excellent botanist, Aug. St. Hilaire. If several 

 trifling characters are always found in combination, though no 

 apparent bond of connection can be discovered between them, 

 especial value is set on them. As in most groups of animals, 

 important organs, such as those for propelling the blood, or for 

 aerating it, or those for propagating the race, are found nearly 

 uniform, they are considered as highly serviceable in classification ; 

 but in some groups all these, the most important vital organs, are 

 found to offer characters of quite subordinate value. Thus, as 

 Fritz Mullerhas lately remarked, in the same group of crustaceans, 

 Cypridina is furnished with a heart, whilst in too closely allied 

 genera, namely Cypris and Cytherea, there is no such organ ; one 

 species of Cypridina has well -developed branchiae, whilst another 

 species is destitute of them. 



We can see why characters derived from the embryo should be 

 of equal importance with those derived from the adult, for a 

 natural classification of course includes all ages. But it is by no 

 means obvious, on the ordinary view, why the structure of the 

 embryo should be more important for this purpose than that of 

 the adult, which alone plays its full part in the economy of nature, 

 "ict it has been strongly urged by those great naturalists, Milne 

 Edwards and Agassiz, that embryological characters are the most 

 important of all ; and this doctrine has very generally been 

 admitted as true. Nevertheless, their importance has sometimes 

 been exaggerated, owing to the adaptive characters of larvae not 

 having been excluded ; in order to show this, Fritz Miiller 

 arranged by the aid of such characters alone the great class of 

 crustaceans, and the arrangement did not prove a natural one. 

 But there can be no doubt that embryonic, excluding larval 

 characters, are of the highest value for classification, not only 

 with animals but with plants. Thus the main divisions of flower- 

 ing plants are founded on differences in the embryo, on the 

 number and position of the cotyledons, and on the mode of 

 development of the plumule and radicle. We shall immediately 



