1 50 ZOOLOGY 



fish have left recognizable impressions. There are 

 many marine invertebrates, including highly organized 

 Crustacea of numerous kinds, but no vertebrates of any 

 kind, and none of the higher plants. Worms were 

 numerous, and some of them possessed remarkable 

 characters, leglike appendages, bristles, or spines. 

 Appearance J. After some millions of years a vertebrate fauna 

 ^ " appeared, still aquatic, but apparently living in fresh 

 waters. Singular armored forms are found, apparently 

 the ancestors of the fishes. Their exceedingly fragmen- 

 tary remains occur in Colorado and Wyoming, in rocks 

 of Ordovician age. The Cambrian and Ordovician con- 

 stitute the early Paleozoic. In the Middle Paleozoic (Si- 

 lurian and Devonian rocks) 'great changes are observed. 

 The fishes now become abundant ; land plants and 

 arthropods (scorpions) appear. Finally, vertebrates 

 become adapted to a partly terrestrial life, and am- 

 phibians are developed. We now come to the Late 

 Paleozoic, often called Carboniferous, that is, coal- 

 bearing. It is divided into Mississippian, P.ennsyl- 

 vanian, and Permian, all periods of long duration. In 

 the Pennsylvanian the great forests and masses of vege- 

 tation gave rise to anthracite coal, but flowering plants 

 were absent. Land vertebrates were becoming numer- 

 ous, and insects swarmed everywhere. The earliest 

 insects were some of them of immense size ; one found in 

 France was about 2 feet 4 inches from wing tip to wing 

 tip. These lasted for a long time, but in middle Penn- 

 sylvanian they died out, and the country was overrun 

 with cockroaches, almost to the exclusion of other in- 

 sect types. In the Permian, however, the land surface 

 in North America was elevated, the climate became 

 cooler, many new families of smaller insects developed, 

 and the cockroaches diminished greatly in numbers and 



