IN THE LIMBS OF MAMMALIA. 5 



mated by the more frequent occurrence of the term homology, especially in the works 

 of Professor Owen, who has done so much toward dispelling the mystery and almost 

 odium attached to the subject, and has cleared up some of its most difficult problems, 1 

 while the philosophy of botany is measured by the term morphology, although it has appar- 

 ently never been perceived that they are corresponding terms, the one relative, the other 

 absolute. 



But much of the wonder vanishes when it is remembered that the unit of vegetable 

 structure is very simple, consisting, in the Dicotyledones, of the phyton, or leaf with its 

 segment of stem ; and that out of these, by wonderful transmutation and combination, the 

 whole plant is built up. The morphology of a vegetable organ is enunciated when it is 

 shown in what manner it is referable to the typical phyton; and since so few elements 

 compose this, seldom would there arise questions of special and thus of general or serial 

 homology. But with animals the case is otherwise. Having left the simple cell, of which 

 vegetables also are composed, we find at once that their bodies are made up of many organs 

 which cannot possibly be referred to any one unit of structure. The nervous, circulatory, 

 and digestive systems are entirely isolated from each other, and differ, not only physiologi- 

 cally, but microscopically and chemically. Still more complex are the relations existing 

 in the muscular and osseous systems, as presented in the Vertebrates ; for here the skele- 

 ton is made up of a series of segments called vertebrae, which are themselves composed 

 of smaller parts or elements having definite relations and bearing distinct names, and by 

 variation in the number, size, and shape of which an almost endless diversity is produced. 

 And now the questions which arise are emphatically those of relation, of homology : what 

 parts represent each other in different animals ; what position one element of a vertebra 

 holds with reference to the others in the same ; and what elements in two different verte- 

 bras repeat each other ; questions of special, of general, and of serial homology, respec- 

 tively. It is not, then, so strange that botanists have used the absolute term morphology with 

 reference to the objects of their study, when so few parts or elements compose the morph 

 or type of which the members of any one large group are built up, as that the anatomist, 

 in his anxiety to determine the manifold relations existing in the bodies of animals, 

 should look upon morphology only as the necessary guide to the more difficult questions 

 of homology, which in itself implies more than one morph. 



Teleological diversities are as of more and less, and the resulting varieties communicate 

 with each other only by continuity ; by continuous degrees. 



Morphological diversities are as of interior and exterior, as of superior and inferior, and the 

 resulting varieties communicate only by contiguity ; by discrete degrees. 



Here, if rightly appreciated, is contained the essence of two most interesting and not 

 always easily understood generalizations, which are potent weapons of the modern zoolo- 

 gist : the one defensive of his belief in a natural classification, the other offensive against 

 those who assert the existence of a regular, uninterrupted succession of organic forms from 

 lowest to highest, because, forsooth, they cannot see how else creation was effected ; thus 

 profanely daring to limit Infinite power by their own wilfully diminished capacity. 



1 In his elaborate and admirable Report on the Homolo- another vertebra before or behind, its serial homology is given. 



yies of the Vertebrate Skeleton, Professor Owen defines three 3d. When a part is said to have the same relations in two 



relations of homology: "1st. When a part is said to occu- different animals, then its special homology is indicated." 

 py a certain position in its vertebra, its general homology is These definitions, as we shall see, do not cover all relations 



enunciated. 2d. When such a part is said to repeat in its of homology. 

 vertebra that which occupies a corresponding position in 

 2 



