Note 67 — PROGRESSION IN OR THROUGH THE AIR.

According to Dr. Crisp the swallow, martin, snipe, and many birds of passage have no air in their bones (Proc. Zool. Soc., Lond. part xxv. 1857, p. 13). The same author, in a second communication (pp. 215 and 216), adds that the glossy starling, spotted flycatcher, whin-chat, wood-wren, willow-wren, black-headed bunting, and canary, five of which are birds of passage, have likewise no air in their bones. The following is Dr. Crisp’s summary:—Out of ninety-two birds examined he found “air in many of the bones, five (Falconidæ); air in the humeri and not in the inferior extremities, thirty-nine; no air in the extremities and probably none in the other bones, forty-eight.”