316 THE ZOOLOGIST. 



adequately developed for its production. The animal origin of 

 the edible nests is at once detected by simply burning a bit of 

 one ; and ]\Ir. Laidlay informed us that, upon analysis, he found 

 the constituent elements to be those of inspissated saliva.* 

 Looking to a number of them, and more particularly to their 

 under surface, the quantity laid on by the bird at each time, in 

 successive layers to the rim, is in many conspicuously apparent, 

 and this quantity is much more than the salivary glands could 

 well be supposed to elaborate. Each addition consists of a linear 

 collop continued along the whole semicircular rim of the nest, 

 which latter forms generally a shallow saucer, imperfect where 

 afl&xed to the rock, and when completed having the place of 

 attachment on either side much thickened. It is evidently in a 

 very viscid state when laid on, adhesive at first, ductile and 

 tenacious while drying, so that on the upper surface threads of it 

 are pulled forth by the bird, and more or less crossed into a kind 

 of network, as if to bind together the vertical layers, some of 

 which are often partially unadherent. These threads, however, 

 consist of a little additional matter to that originally laid on in 

 the successive marginal deposits. Mr. G. R. Gray writes : — 

 " Tlie formation of the nest differs with the species. Some 

 appear to be formed of flakes or threads cemented together, 

 making an almost solid nest ; others are composed entirely of 

 viscous matter. The exterior exhibits many nearly straight 

 threads, which incline or are attached to each other, strengthened 

 in front by some few short pieces of slender sticks " (this we have 

 never seen). " The interior, which is rather shallow, shows many 

 layers of irregular network, formed of a multitude of threads 

 that cross and recross each other in every direction." 



When newly formed these nests are perfectly clean, of a 

 yellowish white colour, and wholly soluble in water ; but when 

 old they become deeply soiled and mixed with feathers, and their 

 value is immensely deteriorated. Hence, as Marsden remarks, 

 " they are distinguished into white and black, of which the first 

 ai'e by far the more scarce and valuable, being found in the pro- 

 portion of one only to twenty-five. The white sort sells in Cliina 



* J. A. S. xiv. 543. " Upou this suiiiiosition, however," Mr. Laidlay has 

 since added, " I do not see how it could be deposited in the form of layers, 

 as it is. The mechanical structure of the nest may be very nicely exposed 

 by soaking it for a few hom"s in rain-water." 



