33 n. WHAT IS A SPECIES ? 



some of which they may be distinguished from any other 

 plants ; — {secondly) the same characters being repeated in 

 their descendants, during successive generations, for a 

 protracted and indefinite time ; — {thirdly) the individuals 

 not being always strictly alike ; but such variations as do 

 occur, being apparently inconstant and reconvertible ; 

 that is, either known to be so from observation, or 

 inferred to be so from analogy. 



This definition seems to include all that is constant 

 and essential in the mental idea of a species ; namely, 

 mutual resemblance, alienal distinctness, reproduction, 

 reconversion, and permanence ; this latter word being 

 taken in the sense of lengthened or indefinite (but not 

 perpetual) duration. The definition does not abso- 

 lutely exclude (nor is it wished to exclude) the possibility 

 of an eventual mutation or transition or extinction of 

 present species. The inconstancy of varieties, and their 

 reconvertibility to the typical forms, have as yet been 

 well observed only for a very short period, or for a few 

 generations of very few species. We know not how long 

 or how exceptionless this reconvertibility has been. As 

 an alleged fact, it is far more usually inferred or sup- 

 posed, than actually ascertained by an examination suffi- 

 ciently exact and continued. The limits of most species, 

 if not those of all species, and the extent and endurance 

 of their varieties, ought to be considered by sound rea- 

 soners as still unfixed, still unascertained. Looking to 

 this uncertainty, and by way of practical guide towards 

 distinguishing between true and false species, perhaps 

 the leading tests against the latter ought to be added to 

 any explanatory definition of the former. 



A false species (variation, variety, race) is negatived 

 {firstly) by its direct reconversion into another apparent 

 species, either under the same or under different external 



