THE ESCULENT SWALLOW. 99 
Some seem to suppose they are made of shells, de- 
scribing them as marked like these with ridges and 
rugosities, and consisting of numerous cells as if a 
number of shells had been conglutinated together. 
Others say they are composed of seafoam, or of the 
juice of a tree called calambouc. Kempfer again 
tells us he was assured by the Chinese fishers that 
the nests are an artificial production, at least those 
usually sold being nothing but a preparation of ma- 
rine polypi, as isinglass is the dried swim-bladder of 
the sturgeon (Accipenser Huso, and A. Ruthenus). 
It seems impossible to come to any satisfactory 
decision upon statements varying in so many im- 
portant circumstances. Were we to determine the 
substance employed from the concurring testimony 
of numbers, we should certainly fix upon what is in- 
definitely called seafoam. Marsden, indeed, ex- 
pressly affirms, that ‘‘ the birds, during their build- 
ing-time, are seen in large flocks on the beach, col- 
lecting in their bills the foam which is thrown up by 
the surf. Of this there is little doubt, but they con- 
structs their nest, after it has undergone, perhaps, a 
preparation from a commixture with the saliva or 
other secretion with which nature may have pro- 
vided them for that purpose.”* 
But in opposition to this it is urged that the caves 
where the nests are found are not always by the 
seaside. Mr. Crawford, the late British resident at 
the court of the Sultan of Java, who superintended 
for several years the collecting of these nests at 
Karang-Bolang, tells us that ‘ very productive caves 
are found in the interior of the country, and at least 
fifty miles from the sea. It appears probable that 
they are most abundant on the seaside, only because 
caverns are there most frequent and least liable to 
disturbance. This seems to prove that seafoam, or 
other marine production, has no share in the forma- 
tion of the nest ; and the most probable hypothesis is, 
* Marsden’s Sumatra, i., 260. 
