HOMOLOGY AND TELEOLOGY 111 



centre in mammals has therefore a homological significance. 

 The scapula in mammals is an example of what Owen calls 

 a "homologically compound " bone. All those bones which 

 are formed by a coalescence of parts answering to distinct 

 elements of the typical vertebra are "homologically com- 

 pound" (p. 105). On the other hand, "All those bones 

 which represent single vertebral elements are ' Ideologically 

 compound ' when developed from more than one centre, 

 whether such centres subsequently coalesce, or remain 

 distinct, or even become the subject of individual adaptive 

 modifications, with special joints, muscles, etc., for par- 

 ticular offices" (p. 106). The limb-skeleton, corresponding 

 as it does to a single bone of the archetype, is the typical 

 example of a ideologically compound bone. Owen in his 

 definition of teleological compoundness has combined two 

 kinds of adaptation (i) temporary adaptation of bones to 

 the exigencies of development, birth and growth (e.g., develop- 

 ment of long bones from separate centres) ; (2) definitive 

 adaptation of a skeletal part to the functions which it has 

 to perform (e.g., teleological structure of limbs). Such adap- 

 tations are, so to speak, grafted on the archetype. 



Owen's general views on the nature of living things merit 

 some attention. Organic forms, according to Owen, result 

 from the antagonistic working of two principles, of which one 

 brings about a vegetative repetition of structure, while the 

 other, a teleological principle, shapes the living thing to its 

 functions. The former principle is illustrated in the arche- 

 type of the vertebrate skeleton, in the segmentation of the 

 Articulates, in the almost mathematical symmetry of 

 Echinoderms, and the actually crystalline spicules of sponges. 

 It is the same principle which causes repetition of the forms 

 of crystals in the inorganic world. "The repetition of similar 

 segments in a vertebral column, and of similar elements in a 

 vertebral segment, is analogous to the repetition of similar 

 crystals as the result of polarising force in the growth of an 

 inorganic body " (p. 171). This "general polarising force" it 

 is which mainly produces the similarity of forms, the 

 repetition of parts, and generally the signs of the unity of 

 organisation. The adaptive or " special organising force " or 

 ic>e'a, on the other hand, produces the diversity of organic 



