THE PRINCIPAL BIRD GROUPS 65 



anatomical characteristics is the absence of 

 syringeal muscles and their consequent want of 

 voice, the only sounds they make being those pro- 

 duced by clappering or striking the mandibles 

 together. Their habits and mode of reproduc- 

 tion are very similar to those of the Herons, 

 but their white eggs are very characteristic. 

 Some of the more aberrant forms are very 

 interesting, including the Adjutant (Leptoptilus) 

 with its enormous neck pouch ; the Jabiru 

 (Mycteria) standing five feet high, with its bare 

 head and neck ; and lastly the still more extra- 

 ordinary Open-bills (Anastomus), so termed 

 because of the wide gap between the two man- 

 dibles near the point. The curious Shoe-bill 

 (Balaeniceps), and the Hammer-head (Scopus) 

 are aberrant forms, which may possibly be 

 associated with the Storks, although opinion is 

 divided as to their kinship. Perhaps they are 

 deserving of at least family rank. 



Another heterogeneous order is the Pelecani- 

 formes, the Steganopodes of Illiger and some 

 other authorities, included in the same order as 

 the foregoing by others. We include within it 

 the Tropic Birds and Gannets, the Cormorants, 

 Pelicans, and Darters, and the Frigate Birds. 

 They are all aquatic birds, and mostly marine 



