512 ARKIV FÖR ZOOLOGI. BAND 1. 



as so many other featnres that they are the most specialised 

 birds whieh have löst or lose during the development more 

 of the reptilian inheritance than other birds. Not even in 

 these the »highest» birds, however, the bill is a wholly avian 

 structure bnt only an organ transformed throngh specialisa- 

 tion and development, the original elements of which organ 

 already were present in the reptilian ancestors. 



Tryckt den 10 juni 1904. 



Stockholm lfl<M. Kungl. Boktryckeriet. 



