Development AND embeyolo(^y. 455 



tinct species from a common progenitor. Homoplastic 

 structures are the same with those which I have classed, 

 though in a very imperfect manner, as analogous modifica- 

 tions or resemblances. 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 metamor- 

 phosed legs; the stamens and pistils in flowers as metamor- 

 phosed leaves; but it would in most cases be more correct, 

 as Professor Huxley has remarked, to speak of both skull 

 and vertebra?, jaws and legs, etc., as having been metamor- 

 phosed, not one from the other, as they now exist, but 

 from some common and simpler element. Most natural- 

 ists, 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 con- 

 verted into skulls or jaws. Yet so strong is the rppearance 

 of this having occurred that naturalists can hardly avoid 

 employing language having this plain signification. Ac- 

 cording 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 would have retained through inheritance, if 

 they had really been metamorphosed from true though er- 

 tremely simple legs, is in part explained. 



DEVELOPMEJS'T A]S"D EMBEYOLOGY. 



This is one of the most important subjects in the vhole 

 round of natural history. The metamorphoses of insects, 

 with v/hich every one is familiar, are generally effected 

 abruptly by a few stages; but the transformations are in 

 reality numerous and gradual, tliough concealed. A cer- 

 tain ephemerous insect (Chloeon) during its development, 

 moults, as shown by Sir J. Lubbock, above twenty times, 

 and each time undergoes a certain amount of change; and 

 in this case we see the act of metamorphosis performed in 



