35^ THE HISTOKY OF CEEATION. 



their specific form by superficial adaptation to particular 

 local relations. 



Next to the flying animals, those animals, of course, have 

 spread most quickly and furthest which were next best able 

 to migrate, that is, the best runners among the inhabitants 

 of the land, and the best swimmers among the inhabitants of 

 the water. However, the power of such active migrations 

 is not confined to those animals which thi'oughout life enjoy 

 free locomotion. For the fixed animals also, such as corals, 

 tubicolous worms, sea-squirts, lily encrinites, sea-acorns, bar- 

 nacles, and many other lower animals which adhere to sea- 

 weeds, stones, etc., enjoy, at least at an early period of life, 

 free locomotion. They all migrate before they adhere to 

 anything. Their first free locomotive condition of early life 

 is generally that of a " ciliated " larva, a roundish, cellular 

 corpuscle, which, by means of a garb of movable " flimmer- 

 hairs," (Latin, " cilia ") swarms about in the water and bears 

 the name of Planula. 



But the power of free locomotion, and hence, also, of active 

 migration, is not confined to animals alone, but many plants 

 likewise enjoy it. Many lower aquatic plants, especially the 

 class of the Tangles (Alg?e), swim about freely in the water 

 in early life, like the lower animals just mentioned, by 

 means of a vibratile hairy coat, a vibrating whip, or a 

 covering of tremulous fringes, and only at a later period 

 adhere to objects. Even in the case of many higher plants, 

 which we designate as creepers and climbing plants, we may 

 speak of active migration. Their elongated stalks and 

 perennial roots creep or climb during their long process 

 of growth to new positions, and by means of their wide- 

 spread branches they acquire new habitations, to which 



