280 HABIT AND INTELLIGENCE. [chap. 



Value in -while, on the other hand, organs which have become rudi- 

 tirafo/^" i^entary, and therefore useless, like the nails under the 

 rudiment- skin of the manati (an aquatic mammal), are regarded by 

 ' the best authorities as of importance at least equal to that 

 of organs homologous with them, but in a state of func- 

 and of tional perfection and activity. " It may even be given as 

 connected ^ general rule, that the less any part of the organization 

 ■w^tli. is connected with special habits, the more important it 



ST) 6 013.1 



habits. becomes for classification." ^ " With plants, how remark- 

 able it is that the organs of vegetation, on which their 

 whole life depends, are of little signification excepting in 

 [separating the whole vegetable kingdom mto] the first 

 main divisions ; whereas the organs of reproduction, with 

 their product the seed, are of paramount importance." ^ 



If we believe in the theory of the origin of species by 



development — or, to use more accurate language, if we 



believe that different species have been derived from a 



common ancestor by descent with different modifications — 



all this, and much more, at once becomes intelligible. 



The deve- Before the " development theory " became familiar to sci- 



themv^*^ entific men, and wliile the origin of species was regarded 



explains as sometliing inscrutable, like the origin of matter or of 



all this. . . . 



life, though naturalists were instinctively certain that 



their words had a true and important meaning when they 



spoke of true classification and of real affinities, yet they 



found it impossible to state what that meaning was, in a 



way that was satisfactory even to themselves. But if the 



development theory is true, real affinity simply means 



affinity of kindred by descent, and true classification is by 



Affinity genealogy. When we say, for instance, that the Cirrhipedes, 



kindred • °^ Barnacles, though totally unhke in form and appearance, 



as of are proved by the character of their larvae to be closely 



Cirrlii" 



pedes connected with the Crustacea, what we mean is, that they 

 to Crusta- are literally akin to the Crustacea, being descended from 



ceans. "' . 



Groups crustacean ancestors. Not only every species but every 



within genus is descended from a single ancestor ; all the genera 



^ . of an order are descended from a single ancestor further 



back ; so of all the orders of the same class, and all the 



^ Darwin's Origin of Species, p. 489. ' Ibid. p. 490. 



