238 MOEPHOLOGY. [Chap. XIV. 



adduces the close resemblance of the parts on the right 

 and left sides of the body, and in the successive 

 segments of the same mdividual animal; and here we 

 have parts commonly called homologous, which bear 

 no relation to the descent of distinct species from a 

 common progenitor. Homoplastic structures are the 

 same with those which I have classed, though in a very 

 imperfect manner, as analogous modifications or re- 

 semblances. Their formation may be attributed in part 

 to distinct organisms, or to distinct parts of the same 

 organism, having varied in an analogous manner ; and 

 in part to similar modifications, having been preserved 

 for the same general purpose or function, — of which 

 many instances have been given. 



Naturalists frequently speak of the skull as formed 

 of metamorphosed vertebrae ; the jaws of crabs as 

 metamorphosed legs ; the stamens and pistils in flowers 

 as metamorphosed leaves ; but it would in most cases 

 be more correct, as Professor Huxley has remarked, to 

 speak of both skull and vertebrae, jaws and legs, &c, as 

 having been metamorphosed, not one from the other, as 

 they now exist, but from some common and simpler 

 element. Most naturalists, however, use such language 

 only in a metaphorical sense ; they are far from meaning 

 that during a long course of descent, primordial organs 

 of any kind — vertebrae in the one case and legs in the 

 other — have actually been converted into skulls or jaws. 

 5 30 strong is the appearance of this having occurred, 

 that naturalists can hardly avoid employing language 

 having this plain signification. According to the views 

 here maintained, such language may be used literally ; 

 and the wonderful fact of the jaws, for instance, of a 

 crab retaining numerous characters which they probably 



