CLASSIFICATION 225 



1 * sub-varieties differ in tlie important character of the 

 length of the beak, yet all are kept together from having 

 the common habit of tumbling; but the short-faced breed 

 has nearly or quite lost this habit: nevertheless, without 

 any thought on the subject, these tumblers are kept in 

 the same group, because allied in blood and alike 

 in some other respects. 



With species in a state of nature, every naturalist 

 has in fact brought descent into his classification; for 

 he iacludes in his lowest grade, that of species, the two 

 sexes' and how enormously these sometimes differ in the 

 most important characters is known to every naturalist: 

 scarcely a single fact can be jjredicted in common of the 

 adult males and hermaphrodites of certain cirripeds, and 

 yet no one dreams of separating them. As soon as the 

 three Oi'chidean forms, Monachanthus, Mj^anthus, and 

 Catasetum, which had previously been ranked as three 

 distinct genera, were known to be sometimes produced 

 on the same plant, they were immediately considered as 

 varieties; and now I have been able to sbow that the}^ 

 are the male, female, and hermaphrodite forms of the 

 same species. The naturalist includes as one species 

 the various larval stages of the same individual, how- 

 ever much tliey may differ from each other and from 

 the adult, as well as the so-called alternate generations 

 of Steenstrup, which can only in a technical sense be 

 considered as the same individual. He includes monsters 

 and varieties, not from their partial resemblance to the 

 parent-form, but because they are descended from it. 



As descent has universally been used in classing 

 together the individuals of the same species, though 

 the males and females and larvee are sometimes ex- 



