CLASSIFICATION OF FISHES. 461 



Order 2. BrancJiioganoidei (Polypterus). 

 Order 3. Hyoganoidei (Lepidosteus, Arnia). 



Subclass III. Teleostei. Skeleton bony; skull composed of numerous 

 bones ; optic nerves crossing each other ; usually four pairs 

 of gills, with several opercular bones ; heart without a cone, 

 but with an arterial bulb ; intestine generally without a 

 spiral valve ; mostly oviparous. 



Order 1. Opisthomi (Notacanthus). 



Order 2. Apodes (Anguilla). 



Order 3. Nematognatlii (Amiurus). 



Order 4. Scyphophori (Mormyrus). 



Order 5. Teleocephali (Salmo, Perca, Gadus). 



Order 6. Pediculati (Lophius). 



Order 7. Lophobranchii (Hippocampus). 



Order 8. Plectognatld (Tetrodon, Mola). 



Laboratory Work. Fishes should usually be dissected, except when 

 large, under the water ; small specimens can be pinned down to the 

 bottom of cork- or wax-lined dissecting pans, and the more delicate 

 parts worked out with fine scissors and knives. The brain and spinal 

 cord can be dissected with ease, provided care be taken, with scalpel 

 and scissors, as the bones covering them can be cut away by means of 

 gtout scissors and bone-pliers and fine surgical saws. Longitudinal 

 sections will bring out the relations of the brain and beginnings of the 

 nerves, and transverse sections of the tail may be made to show the 

 disposition of the muscles. The skeleton may be prepared whole by 

 removing the flesh carefully from alcoholic or partly macerated speci- 

 mens. Disarticulated skeletons for study can be made by parboiling 

 the fish and then separating the bones from the flesh. To study the 

 circulation, careful injections should be made by the use of an inject- 

 ing syringe, with wax, plaster of Paris, or vermilion as the injecting 

 medium. 



CLASS V. DIPNOI (Lung-fixlt). 



General Characters of Dipnoans.* The luug-fishes are 



so called from the fact that, often being in pools and streams 



liable to dry up, they breathe air directly, having true lungs, 



like those of Amphibians, as well as gills. From the nature 



* Hyrtl, Lepidosiren paradoxa. Prag, 1845. 



