IN THE LIMBS OF MAMMALIA. 49 



and may thus be further modified by other adjectives, so in comparative anatomy, nothing is 

 absolutely morphological or teleological, but only with reference to some organ or function 

 more general above, or more special below ; it is the possibility of the configuration of an 

 organ being modified without change to a corresponding degree in the internal structure 

 and arrangement of parts. Zoologically speaking, it is the possibility of specific modifica- 

 tions of generic ideas, so that from a limited number of substantives, by adjective additions 

 are made designations of many more objects ; and few at this day dare affirm that this is 

 only a matter of human invention for human convenience. 



Every genus represents the morphology of the species embraced within it, and they 

 are teleological modifications of the generic idea ; now this is the relation between each 

 higher group and the next lower ; the further we recede from the species, from the indi- 

 vidual in fact, the more occult and ideal becomes the morphology, till we reach at last the 

 four great groups called types, which, as we shall see hereafter, may even be represented by 

 geometrical figures. How far are these removed from the living sentient individuals which 

 form the other zoological extreme ! And yet it does not follow that the existence of the 

 order, the class, or even the type, is any less real and actual than that of the species or of 

 the individual ; it is less material, but none the less substantial ; in fact, the higher the group, 

 the more real and enduring it is, for it exists in all the members of all the groups embraced 

 within it, though it would exist if it had but a single individual representative. 



It was said above, that morphology refers only to the general plan of structure ; in a 

 certain sense this is so, since it refers to a more hidden interior grade of anatomical charac- 

 ters than those which ordinarily appear upon the surface. The zoologist will see that each 

 of his categories of structure is based upon a different grade of morphology ; thus there is 

 a type morphology, the most interior of all, beyond which there are no homologies, but 

 within which are more and more apparent ones, the class homologies, the ordinal homol- 

 ogies, the homologies of the family, genus, and species. I do not mean to say that these 

 groups, as at present characterized by Professor Agassiz, or by any other naturalist, are the 

 true ones, or that they should bear these names, or even that there is just this number of 

 categories of structure; but I do believe that a classification does exist in Nature entirely 

 independent of human thought; that the various kinds of groups in this natural classifica- 

 tion are founded upon categories of structure radically distinct, not at all merging or inter- 

 changing ; and finally, that these categories are simply statements of the various grades of 

 morphology, upon which alone classifications are based. 



But though this seems to carry us away from direct material function or use, it by no 

 means negatives the idea that each natural group does really represent some use in the 

 grand operations of Nature. Indeed, this would follow as the converse of what was said 

 above, that every higher group represents the morphology of the groups next below, which 

 are themselves teleological modifications of it ; conversely, each lower group is, with 

 reference to the next higher, more directly teleological, and increasingly so as we ap- 

 proach the species and the individual. Even the types, ideal and unsubstantial as they 

 seem, represent the four ways in which the powers of sensation and voluntary motion 

 may be embodied and brought into use in the economy of Nature : the idea of an animal 

 is distinct enough in our minds, but so hard to put into words that no really satisfactory 

 definition has ever been proposed. What better evidence of the immaterial character of 

 the principle which distinguishes the animal from the vegetable and mineral subdivisions 

 of Nature. 



It seems at first rather strange that the progress in philosophical anatomy may be esti- 



MEMOIRS BOST. SOC. NAT. HIST. Vol. I. 13 



