CONCLUDING REMARKS. 439 



tion of decrease; that there is a limit in the direction 

 of increase of structure, or to positive Variations, for 

 no more Variations can occur in any species, than that 

 amount of characters or features which such species 

 once lost; that there is a limit in the direction of de- 

 crease of structure, or to Degeneration, or negative 

 variations, because any organism which falls short of the 

 full organic complement of its species, has thereby en- 

 tailed upon it, a proportional physiological, evil effect, 

 while if such modification of the specific type be carried 

 beyond what is a comparatively very narrow margin, 

 the effect upon the fertility and constitutional vigor of 

 the individual will be such as to entail the extinction of 

 its line, and death to itself; that the structural degenera- 

 tion which has taken place under nature, in almost 

 every species, has been in derogation of the physiologi- 

 cal integrity of the individuals, and this is evidenced by 

 the evil effects which accompany the close-interbreed- 

 ing of individuals of each such species ; that each and 

 every return which is made towards the full structural 

 complement, viz.j the original perfect type, — made, 

 either, by means of direct Reversion, or positive Va- 

 riation, by means of Crossing (whereby the offspring 

 has, contributed to it by either parent, a character or 

 characters which the other parent lacked), or by means 

 of Grafting, — is fraught with proportional increase of 

 physiological good, or fraught, rather, with propor- 

 tional abatement of the evil which was caused by the 

 departure from such normal build. 



The obvious import of this law, of proportionate de- 

 velopment, is that each species is normally immutable. 



