382 ON THE ORIGIN OF SPECIES 



common of the males and hermaphrodites of certain 

 cirripedes, when adult, and yet no one dreamg of 

 separating them. The naturalist includes as one species 

 the several larval stages of the same individual, however 

 much they may differ from each other and from the 

 adult ; as he likewise includes the so-called alternate 

 generations of Steenstrup, which can only in a technical 

 sense be considered as the same individual. He 

 includes monsters ; he includes varieties, not solely 

 because they closely resemble the parent - form, but 

 because they are descended from it. He who believes 

 that the cowslip is descended from the primrose, or 

 conversely, ranks them together as a single species, 

 and gives a single definition. As soon as three 

 Orchidean forms (Monochanthus, Myanthus, and Cata- 

 setum), which had previously been ranked as three 

 distinct genera, were known to be sometimes produced 

 on the same spike, they were immediately included as 

 a single species. 



As descent has universally been used in classing 

 together the individuals of the same species, though 

 the males and females and larv» are sometimes ex- 

 tremely different ; and as it has been used in classing 

 varieties which have undergone a certain, and some- 

 times a considerable amount of modification, may not 

 this same element of descent have been unconsciously 

 used in grouping species under genera, and genera 

 under higher groups, though in these cases the modi- 

 fication has been greater in degree, and has taken a 

 longer time to complete? I believe it has thus been 

 unconsciously used ; and only thus can I understand 

 the several rules and guides which have been followed 

 by our best systematists. We have no written pedi- 

 grees ; we have to make out community of descent by 

 resemblances of any kind. Therefore we choose those 

 characters which, as far as we can judge, are the least 

 likely to have been modified in relation to the con- 

 ditions of life to which each species has been recently 

 exposed. Rudimentary structures on this view are as 

 good as, or even sometimes better than, other parts of 



