PERCHING BIRDS. 175 



nightjar cannot effect any grasp of the bough as it sits 

 lengthwise, and therefore the necessary firm position is 

 obtained in other ways. It will be seen by any one who 

 will take the trouble to examine it, that the serratures 

 on the centre claws ate therefore placed in exactly the 

 best position for preventing the foot from slipping side- 

 ways ; and this is still further provided against by the 

 hind toe projecting forwards and inwards so much so, 

 indeed, that it has the appearance of being inserted on 

 the inner side of the foot ; and the whole organ is thus 

 admirably adapted for its designed use. 



It is worthy of remark, as tending to corroborate my 

 theory, that there are one or two Australian species 

 (Podargus and jEgotTieles), and at least one in South 

 America, which have the middle claw smooth and the 

 hind toe directed backwards. This variation in struc- 

 ture leads, as might be expected, to a corresponding 

 difference in the use of the organ ; and we consequently 

 find that they do not perch sideways, but across, and 

 also hop from bough to bough. 



I do not put this view forward as the undoubted solu- 

 tion of the disputed point, but think that from both 

 positive and negative evidence the probabilities are in 

 its favour. 



There is a peculiarity about the jarring note of the 

 nightjar which I have never seen mentioned by any 

 writer. This peculiar sound consists of two notes, ut- 

 tered alternately one a third lower than the other 

 the highest being evidently made when the breath is 

 expelled, and the lowest when it is inspired ; and thus 

 the jar is continued without intermission for a much 

 longer time than would otherwise be possible. 



Mr. Jesse, in his Gleanings, says, "they continue their 



