14+ THE CHAIN OF LIFE. 



come on the stage in three familiar generic forms, similar to 

 those which still live, but all of small size, indicating perhaps 

 that the conditions were less favourable for such creatures than 

 those of the temperate and warmer climates at present. It may 

 seem a small step in advance for Sea-snails to lose their gills 

 and to become Land-snails, and this without any elevation ol 

 their general structure; but it must be borne in mind that we 

 have here not only the dropi)ing of the gills for an air-sac, but 

 profound changes in teeth, mucous glands, shell, and other par- 

 ticulars, to fit them for new food and new habits. Tt is also 

 singular that the Land-snails at once ai)pcar instead of the 

 intermediate forms of the air breathing fresh-water snails. 

 These last may, however, yet be found. ^ 



The Millepedes, like the Land-snails, were f;rst found in the 

 Coal-formation of Nova Scotia, but species ha/e since been 

 discovered not only in Illinois, but also in Greai Dri^^ain and 

 in Bohemia. In Nova Scotia alone two genera and five dis- 

 tinct species have been found, all in the interior of erect trees, 

 to which these creatures probably resorted for food and shelter 

 (Fig. 126). All the species yet known are allied to the modern 

 Gallyworms, though presenting distinct features which seem to 

 separate them as a distinct family,^ and were probably vegetable- 

 feeders. One of the Western species has the peculiarity, un- 

 known among its modern successors, of being armed .vith long 

 spines.^ The moist, equable climate and exuberant vegeta- 

 tion of the Coal-period would naturally be very favourable to 

 Millepedes, and it is likely that the discoveries made as yet 

 give but a faint idea of their actual abundance. It is not 

 improbable that they subsequently declined, as we know of 

 none between the Carboniferous and the Jurassic, and they 

 do not seem to have improved up to the modern period. The 



1 Recent large acquisitions of material from the erect trees of the South 

 Jopgins may, I hope, soon enable me to add to the number of species of 

 L^nd-snails of the Carboniferous. 



* ArchiulidcB of Scudder. 



* Euphobeda armii^era (Meek and Worthen), from Illinois. 



