208 THE ORIGIN OF SPECIES 



cess, to another part; thus it is difficult to get a cow to 

 give much milk and to fatten readily. The same varie- 

 ties of the cabbage do not yield abundant and nutritious 

 foliage and a copious supply of oil-bearing seeds. When 

 the seeds in our fruits become atrophied, the fruit itself 

 gains largely in size and quality. In our poultry, a 

 large tuft of feathers on the head is generally accom- 

 panied by a diminished comb, and a large beard by 

 diminished wattles. With species in a state of nature 

 it can hardly be maintained that the law is of universal 

 application; but many good observers, more especially 

 botanists, believe in its triith. I will not, however, here 

 give any instances, for I see hardly any way of distin- 

 guishing between the effects, on the one hand, of a part 

 being largely developed through natural selection and 

 another and adjoining part being reduced by this same 

 process or by disuse, and, on the other hand, the actual 

 withdrawal of nutriment from one part owing to the 

 excess of growth in another and adjoining part. 



I suspect, also, that some of the cases of compensa- 

 tion which have been advanced, and likewise some other 

 facts, may be merged under a more general principle; 

 namely, that natural selection is continually trying to 

 economize every part of the organization. If under 

 changed conditions of life a structure, before useful, 

 becomes less useful, its diminution will be favored, for 

 it will profit the individual not to have its nutriment 

 wasted in building up a useless structure. I can thus 

 only understand a fact with which I was much struck 

 when examining cirripeds, and of which many analogous 

 instances could be given: namely, that when a cirriped 

 is parasitic within another cirriped and is thus protected, 



