Chap. II. ORDERS AMONG ANIMALS. 153 



tainetl, its limits better defined, when we know all its representatives; but T am 

 satisfied that any natural genus may be at least pointed out, however numerous 

 its species may be, from the examination of any single one of them. Moreover, 

 the number of genera, both in the animal and vegetable kingdom, which contain 

 but a single species, is so great that it is a matter of necessity in all these cases 

 to ascertain their generic characteristics from that one species. Again, such species 

 require to be characterized with as much precision, and their specific characters to 

 be described with as much minuteness, as if a host of them, but not yet known, 

 existed besides. It is a very objectionable practice among zoologists and botanists, 

 to remain satisfied in such cases with characterizing the genus, and perhaps to 

 beheve, what some writers have actually stated distinctly, that in such cases generic 

 and specific characters are identical. 



Such being the natural relations and the subordination of types, classes, orders, 

 families, genera, and species, I believe, nevertheless, that neither types, nor classes, 

 (orders of course not at all,) nor families, nor genera, nor species have the same 

 standing when compared among themselves. But this does not in the least inter- 

 fere with the prominent features of orders, for the relative standing of tj-pcs, or 

 classes, or families, or genera, or species does not depend upon the degrees of 

 comphcation of their structures as that of orders does, but upon other features, 

 as I will now show. The four great types or branches of the animal kingdom, 

 characterized as they are by foiu- different plans of structure, will each stand higher 

 or lower, as the plan itself bears a higher or lower character, and that this may 

 be the case we need only compare Vertebrata and Radiata.* The different classes 

 of one type will stand higher or lower, as the ways in which and the means with 

 which, the plan of the type to which they belong is carried out, are of a higher 

 or lower nature. Orders in any or all classes are of course higher or lower 

 accorduig to the degree of perfection of tlieir representatives, or according to the 

 complication or simplicity of their structure. Famihes may stand higher or lower 

 as the peculiarities of their form are detenniued by modifications of more or less 

 important systems of organs. Genera may stand higher or lower as the structural 

 pecuharities of the parts constituting the generic characteristics exhibit a higher 

 or lower grade of development. Species, lastly, may stand one above the other, 

 in the same genus, according to the character of their relations to the surrounding 

 world, or that of their representatives to one another. These remarks nuist 

 make it plain that the respective rank of groups of the same kind among them- 

 selves must be detennined by the superior or inferior grade of those features upon 



* I must leave out the details of such comparisons, moreover, any text-book of comparative anatomy 

 as a mere mention of tJie point suffices to suggest them ; may furnish the complete evidence to that effect. 



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