This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1917 Excerpt: ...1003, pp. 731-736. Gadow, H., Amphibia and Reptiles, Cambridge Natural History, Vol. VIII, 1909. CHAPTER XXII Volant Adaptation Next to water as a moulding environment comes the air, for the creature which inhabits either is surrounded on all sides by a homogeneous medium so that it becomes uniformly and beautifully modified to offer the least possible resistance to the attainment of speed. Waterjnhabiting forms, however, whether primarily or secimclarjly_dapted, may become so thoroughly at home that in the latter group no evidence, of their former habitat may be outwardly visible. Aerial crealureSjon the contrary, are heVgr6xclusiyejy.ucji_ajidjnust return to flic trees or earth or sea when they wish to rest. Hence their adaptation, is always a double one and as a consequence cannot reach the extreme of specialization / of water-lDorneTypes. Classification of Flight Passive or Gliding Flight.--Flight is_QjLtwo sorts.:, fksL passive or gliding flight, wherein, with the exception of the.fishes, the cfeatuie meiely takes an initial leap from a high point and, held up by certain sustaining organs and impelled by gravity, glides to a lower level, sometimes covering a horizontal distance of many yards. Aside from the initial impetus there is no locomotive force other than gravity, so that the flight is comparable to a gliding aeroplane bereft of its engine power. True Flight.--True flight, on the contrary, implies powerj.so thajTthere is sustained movement through the air, whether the flight be brief like thatadorncstic hen or supported on the tireless pinions of an albatross. True flight has evolved three times aJ71ong vertebratesin the-teptilian pterodactyls, the birds, and the bats. Whether flying fishes should be included is a much disputecTquestion. True fly.
