ORIENTATION 



ered by an operculum. An air bladder is found in most species. Paired fins 

 are not supported by a median axis. 



Series 1. The Ganoidei. The ganoid fishes, possessing ganoid or cycloid 

 scales. An air bladder is to be found with an open duct united to the post- 

 pharyngeal area. A spiral valve is developed in the intestine. There are two 

 groups of ganoid fishes, viz. the Chondrostei, which possess a cartilaginous 

 skeleton and dermal bony plates, and the Holostei which have a bony skeleton. 



Examples of Chondrostei are Acipenser fulvescens, Scaphirhynchus pla- 

 torhynchus, and Parascaphirhynchus albiis. Lepisosteus osseus and Amia calva 

 are representatives of the Holostei. 



Series 2. Teleostei. In the bony fishes an air bladder is present but usually 

 the pneumatic duct connecting the air bladder with the esophagus is rudi- 

 mentary or absent. A spiral valve is absent in the intestine. The scales are 

 cycloid or ctenoid, and in some instances are absent altogether. 



Examples: Oncorhynchus tschawytscha, the chinook or king salmon, the 

 most important source of food fish in the country; Salmo salar, the Atlantic 

 salmon; Trutta irideus, the rainbow trout; Salvelinus fontinalis, the speckled 

 brook trout, and a host of other genera and species. 



2. Class: Amphibia 



The amphibians are cold-blooded vertebrates adapted to an existence in a 

 watery or moist medium. Some species such as Necturus maculosus and the 

 axolotl, Ambystoma mexicanum, spend their entire life within water, while 

 others such as the frogs and salamanders are in and out of the water. The 

 toads, on the other hand, are able to get along under fairly dry conditions. 

 The skin is soft, moist, and glandular, and, with the exception of the Gymno- 

 phiona, it is devoid of scales. External respiration is carried on by means of 

 gills in the larva, but in the adult the lungs and skin are the principal areas 

 concerned with respiration. However, in those adults which live exclusively 

 in the water, gills may be retained. Some species do not possess lungs and in 

 these the skin and lining surfaces of the pharynx accommodate respiratory 

 functions. In forms such as Necturus and the Axolotl, external gills function 

 as the principal mechanism of external respiration in the adult. Excluding 

 the sinus venosus, a three-chambered heart is typical of the group. 



Order 1 : Caudata (Urodela) 



The salamanders and newts form a large number of amphibian species. 

 They have an elongate body with a conspicuous tail and the body muscles 

 tend to retain a segmental condition. Many vertebrae are present. 



Examples: Cryptobranchus alleganiemis, Triturus viridescens, Ambystoma 

 maculatum, Desmognathus fuscus, Plethodon cinereus, Amphiuma means, 

 Necturus maculatus, Siren lacertina, Triton cristatus, etc. 



