166 AETISTS AND AETISANS IN THE FEATHERED WOELD. 



aration of soups and sauces, and also introduced 

 into this country to be used as extraordinary deli- 

 cacies. They are composed almost entirely of saliva, 

 which in many other cases assists materially in binding 

 together the materials of which nests are composed. 

 In the genus collocallia the salivary glands reach an 

 enormous development, and swell even more at the 

 time of nidification. They secrete a thick, glutinous 

 matter, like mucilage, which can be drawn out in threads, 

 and which hardens to a transparent, whitish mass in the 

 open air. If the birds want to begin their nests, they 

 fly repeatedly against the chosen spot on a perpendicular 

 rock, and' press the saliva against the stone with the tip 

 of their tongues. This they do perhaps twenty or thirty 

 times in rapid succession, whithout going far away, which 

 proves that they do not bring any material from outside, 

 but have it in abundance with them. Thus they build 

 first a semi-circular or horse-shoe shaped structure, the 

 real foundation for the whole nest, which one species, 

 collocallia nidifica, builds of its saliva only, while another 

 one, collocallia fuciphaga, makes use of sea-weeds cast 

 upon the shore by the waves, also glued together by their 

 saliva. The nest of the former consists of a dry, whitish, 

 transparent substance, which is distinctly cross-striped. 

 These stripes run in wave-lines, more or less parallel to 

 each other, and indicate the layers which were put on 

 one at a time. The specimens under the microscope give 

 no evidence of any distinct vegetable structure, nor of 

 any distinctly vegetable product as cellulose. All the 

 relations go to prove that the great mass of the substance 

 was mucine, and such microscopic features as are apparent 

 confirm the view that the nest is formed of strings of 

 mucus plastered together. The mucus, when separated, 

 gives some reactions, different, to a certain extent, from 

 those which are given by ordinary mucine ; but these 

 differences are not great enough to weaken the conclusion 



104 



