INTRODUCTION c 



5. The Ganoid Stage 



(b) Ganoidei. — An ancient group of armored fishes 

 in which the skeleton becomes partly ossified; 

 air-bladder with a persistent open duct present 

 hydrostatic in function and foreshadowing the 

 lungs. Abundant in Devonian and Carbonifer- 

 ous times. Modern representatives are the 

 sturgeon and pike. 



(c) Teleostei.—TxwQ bony-fishes; an offshoot from 

 the main line of evolution devonian to modern 

 times. 



{d) Dipnoi.— Lung or mud-fishes; isolated surviv- 

 ors of a very ancient group of Devonian fishes. 



6. The Amphibian Stage 



2. Amphibia.— Legs instead of fins; lungs replacing 

 gills in adult. Mud tracks attributed to amphib- 

 ians have been found in the Devonian and early 

 carboniferous times but abundant fossils are first 

 found in the latter Carboniferous times. The earlier 

 forms were called stegocephalians on account of a 

 curious bony protection for the skull. One branch 

 which reached its highest development in the Per- 

 mian has been thought by some palaceontologists to 

 be the ancestor of mammals. Many forms reached 

 considerable size. The modern representatives are 

 frogs, toads and salamanders. 



/3 Amniota: Amnion and allantois present; gills never func- 

 tional; fins never present. 



7. The Reptilian Stage 



3. Reptilia. — Whole body covered with scales or plates; 

 poikilothermic, i.e. body temperature more or less 

 changeable with surroundings. Although fossil 

 reptiles have not been found until toward the close 

 of the Paleozoic during the early part of the Per- 



