394 NOTES. 



vertebrae vary in form : in the lowest they are biconcave, like those of Fishes ; 

 in Salamanders they are opisthoccelous : in the Frogs and Toads they are 

 usually proccelous. 



162 Salamanders are often taken for Lizards, but differ in having gills in 

 early life and a naked skin. The Proteus and Siren resemble a tadpole ar- 

 rested in its development. 



163 The Surinam Toad has no tongue. 



164 The posterior pair of limbs is sometimes represented by a pair of small 

 bones ; and the Boas and Pythons show traces of external hind-limbs. 



165 There are some notable exceptions. The Slow-worm is legless, and 

 the Chameleon has a soft skin, with minute scales. 



166 According to Owen ; but Huxley insists that the plastron belongs to the 

 exoskeleton. 



167 Knees always bend forward, and heels always bend backward. 



IBS We cannot claim that this airy skeleton is necessary for flight. The 

 bones of the Bat are free from air, yet it is able to keep longer on the wing 

 than the Sparrow. The common Fowl has a hollow humerus ; while some 

 Birds of long flight, as the Snipe and Curlew, have airless bones. 



169 The fossil Archceopteryx, a lizard -like Bird, is placed in a separate 

 division, Saururce. Birds have also been divided according to their degree 

 of development at birth into (1) Hesthogenom, as Fowls, Ostriches, Plovers, 

 Snipes, Rails, Divers, and Ducks, whose chick is hatched completely clothed, 

 has perfect senses, runs about, and feeds itself. When full grown, it uses its 

 first opportunity to settle on land or water, not on trees; the male is po- 

 lygamous and pugnacious ; the female makes little or no nest ; and neither 

 sex sings. This group is of the best use to man, and approaches more nearly 

 to Mammals, the habitual use of the legs and preference for land or water 

 degrading it as a Bird and raising it in the list of animals ; (2) Gymnogenous, 

 as Gulls, Pelicans, Birds of Prey, Herons, Sparrows, Woodpeckers, and 

 Pigeons, whose chick comes helpless, blind, and naked ; it can neither walk 

 nor feed itself, but gapes for food ; the adult is monogamous, and builds 

 elaborate nests in trees and perches; many sing; all are habitual flyers. 

 These are birds par excellence, gifted with higher intelligence than the others, 

 and are never domesticated for food. 



170 Hopping is characteristic of and confined to the Perchers ; but many of 

 them, as the Meadow-lark, Blackbird, and Crow, walk. 



171 This order is artificial. But it is better to retain it until ornithologists 

 agree upon some natural arrangement. The classification of birds is taken 

 from Coues's " Key to North American Birds," as being the work on orni- 

 thology in most general use. 



172 The whales are hairy during foetal life only. 



178 The Manatee has 6; Hoffmann's Sloth 6; and two species of three-toed 

 Sloth have respectively 8 and 9. 



174 As in the Whale, Porpoise, Seal, and Mole. Teeth are wanting in the 

 Whalebone Whales, Ant-eaters, Manis, and Echidna. 



176 The Monotremes resemble Marsupials in having marsupial bones, but 

 have no pouch. They differ from all other Mammals in having no distinct 

 nipples. 



