The President's Address. By Dr. H. Woodward, 141 



Another interesting order are the Dipnoi, or double-breathers, 

 in which both the gills and the air-bladder, which serves the 

 purpose of a lung, are present, and take part in respiration. 



The modern Lepidosiren of South America, the Protopterus of 

 South African rivers, and the Ccratodus (or "Mud-fish") of the 

 Australian rivers, are living examples of this type. 



Teeth, like those of the living Ceratodus, occur in the older 

 "Secondary formations in both hemispheres, and similar teeth, 

 known as Ctenodus, occur in the Carboniferous and Permian rocks. 



The true fishes, with well-developed paired fins and jaws, the 

 €rossopterygii and the Actixopterygii, are characterised by the 

 presence of external ganoine-coated bony plates, with a more or 

 less notochordal skeleton, or only a thin bony tube to the vertebrae 

 and a gelatinous centre. 



Others, like Platysomus, Dapedius and Lepidotus, had a com- 

 pact dermal covering of thickly enamelled bony scales. 



Similarly-armoured fishes like Aspidorhynchus, from the Solen- 

 hofen lithographic limestone, still exist, such as the bony pike of 

 the American rivers. 



The great majority of the Fishes in Secondary and, Tertiary 

 times, like our modern bony-framed fishes, were Teleostomi. 



Fishes with a complete bony skeleton, and in which the gills 

 are but feebly separated, and open into an external cavity covered 

 by a bony operculum, are, with few exceptions, homocercal tailed. 



With the exception of the Dipnoi, all the Fishes are purely 

 aquatic in their habits, and breathe simply by gills, and cannot 

 sustain life for any long period out of the water. 



Amphibia. — The earliest vertebrates which show by the arrange- 

 ment of the nares that they breathe by means of lungs (at least in 

 the adult state) belong to the Amphibia. This group of animals are 

 distinguished from true reptiles by the fact that the young undergo 

 certain metamorphoses after leaving the egg. At this early stage of 

 their existence they breathe by means of external gills, which are 

 occasionally retained along with internal lungs in the adult animal, 

 and one or more pairs of limbs may be wanting. When present, 

 they have the same bones as in the limbs of higher animals ; they 

 are never converted into fins ; the skull has two occipital condyles ; 

 the mandible articulates directly with the skull ; teeth are commonly 

 present on the premaxilla, the maxilla, the vomer, and the dentary 

 bone of the mandible ; they are usually achylosed to the bone, and 

 are simple in structure, but more complex in Ldbyrinthodon ; only 

 two vertebrae are coalesced to form the sacrum ; sometimes the 

 backbone is unossified, forming a mere ring of bone, the interior 

 being gelatinous, a form of backbone called notochordal. 



The earliest of these Amphibians are found in the Coal Measures, 

 Lsuch as Anthracosaurus, represented by Zoxomma, and Archegosaurus. 



