1952 Classification. 



the structure of an animal body, are not only manifested in the con- 

 stant accompaniment of one adaptive modification, by another whose 

 co-existence is necessary for the perfection of the contrivance, but in 

 the essential characters are even still more striking ; peculiarities mi- 

 nute, and to appearance trifling, accompanying those of evidently 

 great importance to the organization, with such unvaried constancy 

 as to be fully as worthy of the confidence of the systematist as the 

 more important characters themselves. It seems probable that, next 

 to the differences presented by the vital parts, those of the osseous 

 system in the vertebrate series (and by analogy, not unlikely, the ex- 

 ternal casing among the articulated division) would be easiest to per- 

 ceive, and most to be depended on, from the permanence of their 

 form, the facility of preservation, and from such being the only parts 

 left for our observation of the species which have become extinct ; 

 but even these harder organs show the essential and adaptive charac- 

 ters so intimately mixed together, that a very extensive series of ob- 

 servations, aided by a knowledge of the relations they possess to the 

 other parts of which the animal consists, and combined with very 

 sound and careful judgment, is absolutely necessary before any results 

 worthy of our confidence can be arrived at. These remarks may per- 

 haps derive some little support from the circumstance, that in all 

 cases where a generalization has been fully and clearly demonstrated 

 to be a law of nature, it has been, after a long and detailed course of 

 observations, carefully made, and summed up with the soundest of 

 human skill and judgment. 



The mention of some well-known instances may here again be use- 

 ful, in illustration both of the meaning intended and of the manner in 

 which the essential characters were occasionally perceived, and so 

 often overlooked, by the older authors. The order Cetacea will serve 

 this purpose well : all systeraatists have agreed in placing these ani- 

 mals among Mammalia, notwithstanding their wide difference of form 

 from that of others of the class, perceiving that warm blood, pulmo- 

 nary respiration, viviparous generation (in its true sense) and lactation, 

 were essential characters of the class, being combined constantly in 

 it, and not in any other, not even one of them obtaining in that which 

 in external form the Cetacea most resemble; but even the illustrious 

 Cuvier failed to perceive, that those species which he denominated 

 " herbivorous Cetacea " belong truly (as is acknowledged by many of 

 the more philosophic zoologists of the present day) to the order that 

 he called Pachydermata; the simple absence of hind extremities, 

 from its conspicuity, causing the close resemblance to the last-named 



