INTRODUCTION. xi 



interest inci'eases when we leam that Hesperornis, one of 

 the ancient toothed - birds (of Cretaceous times) had a 

 similarly effective spur, but made in a slightly different 

 way from that seen in either Diver or Grebe. The re- 

 semblance is deep enough to link the modem Divers and 

 Grebes (Colymbidse) to the Hesperornis of the Chalk ; but 

 the details of the adaptation are different in the three 

 cases. 



Study of Everyday Functions. 



Another line of study is that which inquires into 

 the everyday activities of the birdVbody; and although 

 this requires specialised training and methods if it is to 

 be followed far, no serious student of birds can afford to 

 ignore it, and there is much to be discovered by the 

 ordinary observer who is humble enough to be patient 

 and precise. Let us take an illustration. Birds often 

 drink considerable quantities of water. How do they get 

 rid of this ? They certainly do not sweat, and there is 

 almost no water in the waste that they void. The usual 

 answer to this question is that there is a sort of ' internal 

 pei-spiration ' in the beautiful, soap-bubble-like air-sacs 

 which surround the lungs and are directly connected with 

 them. These very characteristic sacs, which are often con- 

 tinued into the bones, are certainly not of much import- 

 ance in lightening the bird ; they help to increase the 

 high respiratory efficiency of the lungs (in a way which 

 cannot be very briefly explained), and by their ' internal 

 perspiration ' they seem to help in the regulation of the 

 temperature of the body. It is evident that a problem 

 of this sort — for it is by no means finished yet — will 

 require some expert physiological skill. 



On the other hand, one would think that patience and 

 a little ingenuity would suffice to throw some much- 



