252 THE ORiam of species 



provide for itseU. TLie period of activity may come on 

 earlier or later m life; but whenever it comes on, the 

 adaptation of the larva to its conditions of life is just 

 as perfect and as beautiful as in the adult animal. In 

 how important a manner this has acted, has recently 

 been well shown by Sir J. Lubbock in his remarks on 

 the close similarity of the larvse of some insects belong- 

 ing to very different orders, and on the dissimilarity of 

 the larvae of other insects within the same order, accord- 

 ing to their habits of life. Owing to such adaptations, 

 the similarity of the larvae of allied animals is sometimes 

 greatly obscured; especially when there is a division of 

 labor during the different stages of development, as when 

 the same larva has during one stage to search for food, 

 and during another stage has to search for a place of 

 attachment. Cases can even be given of the larvae of 

 allied species, or groups of species, differing more from 

 each other than do the adults. In most cases, however, 

 the larvae, though active, still obey, more or less closely, 

 the law of common embryonic resemblance. Cirri peds 

 afford a good instance of this; even the illustrious Cuvier 

 did not perceive that a barnacle was a crustacean: but a 

 elance at the larva shows this in an unmistakable man- 

 ner. So again the two main divisions of cirripeds, the 

 pedunculated and sessile, though differing widely in ex- 

 ternal appearance, have larvae in all their stages barely 

 distinguishable. 



The embryo in the course of development generally 

 rises in organization; I use this expression, though I am 

 aware that it is hardly possible to define clearly what is 

 meant by the organization being higher or lower. But 

 no one probably will dispute that the butterfly is higher 



