48 PHYSIOGNOMY OF PLANTS. 



396), frogs and toads. Frogs, awakened from winter-sleep 

 by warmth, can support an eight times' longer stay under 

 water without being drowned, than frogs in the breeding 

 season. It Amid seem as if the functions of the lungs in 

 respiration, for some time after their excitability had been 

 suspended, required a less degree of activity. The circum- 

 stance of the sand-martin sometimes burying itself in a 

 morass is a phenomenon which, while it seems not to admit 

 of doubt, is the more surprising, as in birds respiration is 

 so extremely energetic, that, according to Lavoisier's 

 experiments, two small sparrows, in their ordinary state, 

 decomposed, in the same space of time, as much atmo- 

 spheric air as a porpoise. (Lavoisier, Memoires de Chimie, 

 T. i. p, 119.) The winter-sleep of the swallow in question 

 (the Hirundo riparia) is not supposed to belong to the 

 entire species, but only to have been observed in some indi- 

 viduals. (Milne Edwards, Elemens de Zoologie, 1834, p. 

 543.) 



As in the cold zone the deprivation of heat causes some 

 animals to fall into winter- sleep, so the hot tropical coun- 

 tries afford an analogous phseriomenon, which has not been 

 sufficiently attended to, and to which I have applied the 

 name of summer-sleep. (Relation historique, T. ii. pp. 192 

 and 626.) Drought and continuous high temperatures act 

 like the cold of winter in diminishing excitability. In Mada- 

 gascar, (which, with the exception of a very small portion at 

 its southern extremity, is entirely within the tropical zone,) 

 as Bruguiere had before observed, the hedgehog-like Ten- 

 recs (Centenes, Illiger), one species of which (C. ecaudatus) 



