2 
POPULAR HISTORY OP BIRDS. 
female^ who is sometimes fed by lier mate as she sits on the 
nest. 
The young bird has a horny point on the tip of the beak, 
which assists it in breaking the shell ; this falls off a few days 
after exclusion. 
The number of eggs, laid by the various families of birds, 
varies much ; most of the water-birds lay but one egg at a 
time, while the gallinaceous tribes, which supply so much 
food to mankind, lay the greatest quantity, — some, like our 
domestic fowl, continuing to lay many eggs, provided they 
are taken away. 
In birds the respiratory system is particularly perfect. 
Dr. Kaup"^ thus sums up their characteristics in this re- 
spect : — In this class there exists, without any exception, 
an open ear, which is fitted to receive melodious sounds, 
and to repeat them by a particular muscular apparatus on 
the lower larynx. In all birds moreover, some bones even 
take part in the respiration ; in many birds we find oxygen 
to be conducted through air-sacks, even into the intestines, 
in order to bathe them in that element of bird life. No 
class consumes a greater quantity of oxygen than that of 
* 'Contributions to Ornitliology,' for 1849. by Sir V\^illiam Jardine, 
pp. 102, 103. 
