XL.] HABIT AND VARIATION IN HISTORY. 173 



limits of the same language, while their forms remain ; ^ • 

 and this has its parallel in the fact that organs frequently 

 assume new functions, while their form and structure and in 

 undergoes but little change, as in the case of those fishes functions 

 whereof the swim-bladder, without differing much fi'om 

 that of other fishes, assumes the function of limgs. This 

 analogy, or a similar one, is carried much further than we 

 might have expected to find it. We have seen that some 

 animals have rudimentary and totally useless organs, such Eudi- 

 as the leg-bones of some serpents and the wing-bones of the oJ-^anT'^ 

 wingless birds, the only intelligible explanation of which 

 consists in the supposition that they are inherited from 

 ancestors which had the corresponding organs in a deve- 

 loped and working state. ^ These rudimentary organs have 

 been compared to the silent letters used in spelling many compar- 

 words, especially in French and in English. This analogy gijeut" 

 is not merely fanciful, but real. The silent letters were letters. 

 once sounded ; so the rudimentary organs were once, as I 

 believe, developed and at work. The silent letters mark 

 the origin of the word; so, as I believe, do the rudi- 

 mentary organs mark the descent of the species ; and, as 

 all naturalists admit, they mark its true affinities.^ 



Further, there is another very curious parallel between 

 the laws of organic morphology, and the laws of what 



1 As the strangest instance of this tlitit I can think of, I will mention 

 the word implicit. Implicit is properly opposed to explicit, and means im- 

 plied as opposed to expressed : but implicit faith and obedience have come 

 to mean blind faith and obedience. The history of the change in the 

 meaning of the word is this, that implicit faith became a theological ex- 

 pression, signifying the faith which a man was credited with having in a 

 doctrine to which he was too ignorant to attach any meaning, provided he 

 believed in the authority of the Church, on the authority of which the 

 doctrine was to be believed. Thus, a man who was too ignorant or too 

 stupid to know what the Church taught on the subject of transubstantia- 

 tion, would nevertheless be credited withiimplicit or implied faith in that 

 doctrine, provided he only believed that the Church which taught it coxild 

 not err. 



^ See the chapter on Comparative Morphology (Chap. XX. ). 



2 I believe the time will come before very long, when it will be generally 

 admitted that the descent of a species is what constitutes its affinities ; 

 and that affinity iu classification has no meaning except community of 

 descent. 



