The nests of a particular species of swallow which is principally met with in the island of Java, have from time immemorial formed an article of trade between that island and China, where they are purchased at a high price by that voluptuous people, it being believed, that the materials of which the nests are composed, are possessed of an aphrodisiac virtue in an eminent degree. They have been occasionally brought into this country, and are preserved in collections of natural history, as curiosities. In what manner the bird procures the materials out of which the nest is made, has till now remained unknown; a thousand conjectures have, however, been make upon this subject. It has been supposed by some, that it is a gluten collected from the mollusca picked upon the surface of the sea. By others, a substance extracted from certain fuci found on the sea shore. By others again, a portion of the food in a half digested state regurgitated to be employed for this particular purpose. Sir Stamford Raffles, who has just returned from Java, where he resided five years, as lieutenant governor, has brought over a number of these nests, and has been kind enough to offer me some of them, for the purpose of investigating the nature of the materials of which they are composed, and gives it decidedly as his own opinion, that, whatever it is, it is brought up from the stomach, and requires at times so great an effort, as to bring up blood, the stain of which is seen on the nest. This account of Sir Stamford Raffles, in the correctness of whose observation I have the greatest confidence, led me to investigate this subject, and to ascertain by examination whether this particular swallow has any glands that are peculiar to its œsophagus, or stomach, enabling it to secrete a mucus similar in its nature to the substance of which the nest is composed. I at the same time requested my friend, Professor Brande, to analyze one of the nests, and to inform me of its composition. In examining the gastric glands of the Java swallow, even with the assistance of a common magnifying glass, I saw an obvious difference between the appearance of the orifices by which the secretion is poured into the gizzard, and of those of other birds, but, as I had never examined those glands in the common swallow which migrates to this country, it became necessary, before I proceeded farther in the enquiry, to ascertain whether in all the swallow tribe there were similar structures. In the present season this opportunity has been afforded me, and I find that in the common swallow, both male and female, the orifices of the gastric glands differ in nothing from those of birds in general, but that the peculiar structure which I am about to describe is confined to the Java swallow. This bird, Sir Stamford Raffles informs me, does not migrate, but remains all the year an inhabitant of the caverns in that island. Some of the most extensive caves in which they reside, are forty miles from either sea. Those swallows that build their nests near the sea, are observed to fly inland towards extensive swamps where gnats and other insects are in great abundance. Those that build in inland caves, are observed to quit the caves in the morning, and generally return in swarms darkening the air, towards the close of the day; they are, however, going in and out the whole of the day. This bird is double the size of our common swallow. There are two separate nests, one for the male to lie and rest in, which is oblong and narrow, adapted to his form, the other wide and deeper, to receive the female and the eggs.