xix LETTERS TO MARCO 129 



or perched at rest the tail is generally shown 

 forked in far too pronounced a manner. 

 When a swallow is flying swiftly forward the 

 tail is closed, and when at rest or perched 

 the tail is likewise closed, presenting really 

 two straight lines which almost close together. 

 In the case of the house martin or sand 

 martin, if the tail is fully expanded the base 

 line of the fan is nearly straight ; in the tail 

 of the chimney swallow the two outside 

 feathers are much the longest. 



A swallow uses his tail to check his flight, 

 expanding it entirely in stopping, and partially 

 in order to slack or turn, but at full speed it 

 is straight as an arrow. The tail acts both as 

 a rudder and a brake. At rest it is never 

 forked out ; the muscles that spread the tail 

 are extensors and require an effort to keep 

 them in action, just as in our hands we have 

 to exert power to keep the fingers stretched 

 out, but the moment the hand is at rest the 

 fingers close and curl up slightly. 



Numbers of swallows settle every morning 



XJHIVEBSIT-! 



