200 THE BOOK OF NATURE STUDY 



a considerable number of types more nearly related to earth- 

 worms e.g. Tubifex and Nais y live in fresh water ; it seems pro- 

 bable that it was from this stock that the thoroughly terrestrial 

 earthworms took their origin. A similar argument applies 

 in other cases, thus the wood-lice (Oniscm, etc.) are "Isopod" 

 Crustaceans, whose relatives are aquatic and for the most part 

 marine. We can have little hesitation in supposing that the 

 thoroughly terrestrial wood-lice, which have tubular air-passages 

 in some of the abdominal limbs, took their origin from aquatic 

 forms. The tropical cocoanut crab (Birgus latro) is practically 

 terrestrial, except that it returns to the shore to lay its eggs ; it has 

 the upper part of its gill-chamber shut off to make a kind of lung. 

 ' We cannot believe in any abrupt transition from the shore 

 to terra firma. It has been a slow ascent, slow as the origin 

 of dry land itself. Thus mud-inhabiting worms, dwellers in 

 damp humus, bank-frequenting animals, those which find a safe 

 retreat in rottenness or within bolder forms, dot the path from 

 the shore inland. Many have lingered by the way, many have 

 diverged into cul-de-sacs, many have been content to keep within 

 hearing of the sea's lullaby, which soothed them in their cradles." x 



The terrestrial fauna includes some Protozoa, e.g. Amoeba 

 temicola, which lives in moist earth ; some of the Planarians, 

 Nematodes, Leeches, Chaetopods, and other "worms," a few 

 Crustaceans like the wood-lice and the land-crabs, many insects, 

 most of the Arachnids, a legion of shelled snails and shell-less 

 slugs, most adult Amphibians, most Reptiles, many Birds, and 

 most Mammals. Among vertebrates certain fishes, e.g. Perioph- 

 thalmus, are of interest in having learned to gulp mouthfuls 

 of air at the surface of the water, to clamber on the roots of the 

 mangrove trees, or to lie dormant through seasons of drought. 

 But among vertebrates, Amphibians were first to succeed in 

 making the transition from water to dry land. 



We may divide the dry land from the shore inland into (a) links 

 and dunes, (6) meadowland, (c) woodland, (rf) moorland, (e) moun- 

 tain-side. We suppose first, though it is not strategically best, an 

 excursion to the area nearest the seashore, namely, the links. 



We mean by the links the wild area near the shore, between 



1 See (Thomson) p. 222. 



