904 ZOOLOGY. 



the gulls, auks, etc., drop their eggs on bare ground or 

 rocks; as extremes in the series are the elaborate nests of 

 the tailor-bird, and the hanging nest of the Baltimore ori- 

 ole, while the woodpecker excavates holes in dead trees. 

 As a rule, birds build their nests concealed from sight; in 

 tropical forests they hang them, in some cases, out cf reach 

 cf predatory monkeys and reptiles. Birds may change 

 their nesting habits sufficiently to prove that they have 

 enough reasoning powers to meet the exigencies of their 

 life. Parasitic birds, like the cuckoo and cow-birds, lay 

 their eggs by stealth in the nests of other birds. "Some 

 of the swifts secrete from their salivary glands a fluid which 

 rapidly hardens, as it dries on exposure to the air, into a 

 substance resembling isinglass, and thus furnish the ' edi- 

 ble bird's nests' that are the delight of Chinese epicures. 

 In the architecture of nearly all the Passerine birds, too, 

 some salivary secretion seems to play an important part. 

 By its aid they are enabled to moisten and bend the other- 

 wise refractory twigs and straws and git; thorn to their 

 place. Spiders' webs also are employed with groat advantage 

 for the purpose last mentioned, but perhaps chiefly to at- 

 tach fragments of moss and lichen so as to render the whole 

 structure less obvious to the eye of the spoiler. The tailor- 

 bird deliberately spins a thread of cotton and therewith 

 stitches together tlie edges of a pair of leaves to make a 



receptacle for its nest In South America we have a 



family of birds (Furnariithe) which construct on the branch- 

 ing 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 assiduously 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, 



