THE BIRDS. 209 



last mentioned, but perhaps chiefly to attach fragments of 

 moss and lichen so as to render the whole structure less 

 obvious to the eye of the spoiler. The tailor-bird deliber- 

 ately spins a thread of cotton and therewith stitches to- 

 gether the edges of a pair of leaves to make a receptacle for 

 its nest (Fig. 217). . . . In South America we have a family 

 of birds (Furnariidic) which construct on the branching 

 roots of the mangrove globular ovens, so to speak, of mud, 

 wherein the eggs are laid and the young hatched. . . . 

 The females of the hornbills, and perhaps of the hoopoes, 

 submit to incarceration during this interesting period, the 

 males immuring them by a barrier of mud, leaving only a 

 small window to admit air and food, which latter is assidu- 

 ously brought to the prisoners." (Newton.) 



The duties of incubation are, as a rule, performed by the 

 female, but in most Passerine birds and certain species of 

 other groups, the males divide the work with the females- 

 It is in their nesting habits and care for their young that 

 birds greatly surpass fishes and reptiles, and in intelligence 

 they are allied rather to the beasts. In our ascent of the 

 scale of life we have met with no evidences of such high in- 

 telligence, unless we except the social white ants, ants, wasps, 

 and bees. The brains of birds, therefore, as we would ex- 

 pect, are of a much higher type than those of reptiles, for 

 the cerebral hemispheres are greatly increased in size, while 

 the cerebellum is transversely furrowed, and is so large as 

 to cover the entire medulla. 



While there are probably from 7000 to 8000 species of 

 living birds, they are mostly of small size, 5000 species not 

 being larger than a sparrow. And yet each species differs 

 slightly in station or habit from its allies, and thus there 

 are room and food for all. 



Of the whole number of birds known, 878 distinct species 

 or well-marked geographical races inhabit North America 

 north of Mexico and including Greenland. The geographi- 

 cal distribution of birds is somewhat complicated by their 

 migrations. While the larger number of species are tropi- 

 14 



