As I have already mentioned, the Salangana builds her nest of sea-weeds, which she softens in her stomach and then disgorges. During its construction new layers, which soon grow hard in the air, are continually deposited on the margin, until it has attained the proper size. When gathering time approaches, some of the pluckers daily visit the cavern to examine the state of the brood. As soon as they find that most of the young are beginning to be provided with feathers, their operations commence. These nests form the first quality; those in which the young are still completely naked, the second; while those which only contain eggs, and are consequently not yet ripe, rank third. The nests with young whose feathers are completely developed are over-ripe, black, and good for nothing. All the young and eggs are thrown into the sea. The gathering takes place three times a year; the birds breed four times a year. In spite of these wholesale devastations their numbers do not diminish; as many of the young have no doubt flown away before the day of execution, or other swallows from still unexplored caverns may fill up the void. In this manner about 50 piculs are annually collected, which the Chinese pay for at the rate of 4000 or 5000 guilders the picul. Each picul contains on an average 10,000 nests. Dividing these 500,000 nests among three gatherings, and reckoning two birds to each nest, we find that more than 333,000 swallows inhabit at the same time the Javanese coast caverns.
In the interior of the island, in the chalkstone grottos of Bandong, the Salangana also breeds, but in far inferior numbers, as here the annual collection amounts on an average to no more than 14,000 nests. In these inland caves swallows and bats reside together, but without disturbing each other, as the former when not breeding leave their caverns at sunrise, disappear in the distance, and only return late in the evening, when the bats are already enjoying their vespertine or nocturnal flight.
In Sumatra and some other islands of the Indian archipelago, birds'-nests are likewise collected, but nowhere in such numbers as in Java. They are brought to the Chinese market, where they are carefully cleaned before being offered for sale to the consumer. The addition of costly spices renders them one of the greatest delicacies of Chinese cookery, but as for themselves they are nothing better than a fine sort of gelatine.
The Japanese have long been aware that these costly birds' nests are in fact merely softened algæ. They consequently pulverise the proper species of sea-weeds, which are abundantly found on their own coasts, boil them to a thick jelly, and bring them to market under the name of Dschin-schan, as artificial birds'-nests. The Dutch call it Agar-agar, and make great use of it; simple boiling sufficing to convert the dried substance into a thick uniform jelly, which is both nourishing and easy of digestion. Thus we see that the algæ, which the Romans considered so perfectly worthless that, when they wished to express their utter contempt of an object, they declared it to be still viler than the vile sea-weed, are by no means deserving of so hard a sentence. Man himself might be much more justly reproached for neglecting the abundant stores of nourishment which nature has gratuitously provided for him on all flat and rocky coasts. For not only the species I have mentioned are eatable, but also some of the commonest fuci of our seas (Fucus nodosus, F. vesiculosus, Laminaria saccharina), as well as the gigantic alarias and durvilleas of the colder oceanic regions. And yet how rare is their use, notwithstanding the increasing wants of a rapidly growing population!
Surirella constricta.
A. Front view. B. Binary subdivision.—(Highly magnified.)
Besides the larger forms of vegetation, the ocean contains a vast number of microscopical plants. Among these the most remarkable are the Diatomaceæ, simple vegetable cells enclosed in a flinty envelope, consisting of two plates closely applied to each other like the two valves of a mussel. The forms of these minute organisms are no less curious than those of the Foraminifera, for they exhibit regular mathematical figures, and their surface is often most delicately sculptured. Multiplying by spontaneous fissure, many of the Diatoms are met with entirely free after the process of duplicative subdivision has once been completed, while others, such as the Licmophora, or Fan-bearer, an elegant native species, habitually remain coherent one to another, producing clusters or filaments of various shapes, connected by a gelatinous investment or by a stalk-like appendage, which serves to attach them to other plants or to stones and to pieces of wood. Though individually invisible to the naked eye, they appear, when thus congregated, as patches of a green or brownish slimy mass, or as little glittering tufts a line or two in height. Some of their numerous species are natives of fresh water, but by far the majority are denizens of the sea, where they are found from the equator to the poles. The brown scum floating upon the surface of the antarctic waters near the mighty ice barrier which arrested Sir James Ross's progress to the south pole was found to consist almost solely of Diatomaceæ, and they are equally abundant in the Arctic Ocean.
It is remarked by Dr. Hooker that the universal presence of this invisible vegetation throughout the South Polar Seas is a most important feature, since there is a marked deficiency in this region of higher forms of vegetation, so that without the Diatoms there would neither be food for aquatic animals nor (if it were possible for these to maintain themselves by preying on one another) could the ocean waters be purified of the carbonic acid which animal respiration would be continually imparting to it. Thus it is not in vain that they abound in the most inhospitable seas, where but for them no sea-bird would flap its wings, and no dolphin dart through the desert waters.
Licmophora flabellata. (Highly magnified.)