« AnteriorContinuar »
Each of these vestigial organs tells a story of some past adaptation to conditions, one that is no longer needed in the life of the species. They have the same place in the study of animals that silent letters have in the study of words. For example, in our word knight the k and gh are no longer sounded; but our ancestors used them both, as the Germans do to-day in their cognate word Knecht. So with the French word temps, which means time, in which both p and s are silent. The Romans, from whom the French took this word, needed all its letters, for they spelled and pronounced it tempus. In general, every silent letter in every word was once sounded. In like manner, every vestigial structure was once in use and helpful or necessary to the life of the animal which possessed it.
ANIMAL COMMUNITIES AND SOCIAL LIFE 262. Man not the only social animal.—Man is commonly called the social animal, but he is not the only one to which this term may be applied. There are many others which possess a social or communal life. A moment's thought brings to mind the familiar facts of the communal life of the honey-bee and of the ants. And there are many other kinds of animals, not so well known to us, that live in communities or colonies, and live a life which in greater or less degree is communal or social. In this connection we may use the term communal for the life of those animals in which the division of labor is such that the individual is dependent for its continual existence on the community as a whole. The term social life would refer to a lower degree of mutual aid and mutual dependence.
263. The honey-bee.—Honey-bees live together, as we know, in large communities. We are accustomed to think of honey-bees as the inhabitants of bee-hives, but there were bees before there were hives. The “bee-tree” is familiar to many of us. The bees, in Nature, make their home in the hollow of some dead or decaying tree-trunk, and carry on there all the industries which characterize the busy communities in the hives. A honey-bee community comprises three kinds of individuals (Fig. 188) — namely, a fertile female or queen, numerous males or drones, and many infertile females or workers. These three kinds of individuals differ in external appearance sufficiently to be readily recognizable. The workers are smaller than the queens and drones, and the last two differ in the shape of the abdomen, or hind body, the abdomen of the queen being longer and more slender than that of the
Fig. 188.—Honey-bee. a, drone or male ; 0, worker or infertile female ;. c, queen or
male or drone. In a single community there is one queen, a few hundred drones, and ten to thirty thousand workers. The number of drones and workers varies at different times of the year, being smallest in winter. Each kind of individual has certain work or business to do for the whole community. The queen lays all the eggs from which new bees are born; that is, she is the mother of the entire community. The drones or males have simply to act as royal consorts; upon them depends the fertilization of the eggs. The workers undertake all the food-getting, the care of the young bees, the comb-building, the honey-making—all the industries with which we are more or less familiar that are carried on in the hive. And all the work done by the workers is strictly work for the whole community; in no case does the worker bee work for itself alone; it works for itself only in so far as it is a inember of the community.
How varied and elaborately perfected these industries are may be perceived from a brief account of the life history of a bee community. The interior of the hollow in the bee-tree or of the hive is filled with “comb”—that is, with wax molded into hexagonal cells and supports for these cells. The molding of these thousands of symmet
rical cells is accomplished by the workers by means of their specially modified trowel-like mandibles or jaws. The wax itself, of which the cells are made, comes from the bodies of the workers in the form of small liquid drops which exude from the skin on the under side of the abdomen or hinder body rings. These droplets run together, harden and become flattened, and are removed from the wax plates, as the peculiarly modified parts of the skin which produce the wax are called, by means of the hind legs, which are furnished with scissor-like contrivances for cutting off the wax (Fig. 189). In certain of the cells are stored the pollen and honey, which serve as food for the community. The pollen is gathered by the workers from certain favorite flowers and is carried by them from the flowers to the hive in the “pollen baskets,” the slightly concave outer surfaces of one of the segments of the broadened and flattened hind legs. This concave surface is lined on each margin with a row of incurved
Fig. 189.-Posterior leg of stiff hairs which hold the pollen mass se
worker lioney-bee. The curely in place (Fig. 189). The “honey” concave surface of the
upper large joint with is the nectar of flowers which has been
the marginal hairs is sucked up by the workers by means of the pollen basket; the
wax shears are the cuttheir elaborate lapping and sucking
ting surfaces of the mouth parts and swallowed into a sort angle between the two of honey-sac or stomach, then brought
large segments of the to the hive and regurgitated into the cells. This nectar is at first too watery to be good honey, so the bees have to evaporate some of this water. Many of the workers gather above the cells containing
nectar, and buzz—that is, vibrate their wings violently. This creates currents of air which pass over the exposed nectar and increase the evaporation of the water. The violent buzzing raises the temperature of the bees' bodies, and this warmth given off to the air also helps make evaporation more rapid. In addition to bringing in food the workers also bring in, when necessary,“ propolis,” or the resinous gum of certain trees, which they use in repairing the hive, as closing up cracks and crevices in it.
In many of the cells there will be found, not pollen or honey, but the eggs or the young bees in larval or pupal
condition (Fig. 190). The queen moves about through the hive, laying eggs. She deposits only one egg in a cell. In three days the egg hatches, and the young bee appears as a helpless, soft,
white, footless grub Fig. 190. —Cells containing eggs, larvæ, and pupæ of or larva. It is cared the honey-bee. The lower large, irregular cells for hy cortoin of the
for by certain of the are queen cells.-After Benton.
workers, that may be called nurses. These nurses do not differ structurally from the other workers, but they have the special duty of caring for the helpless young bees. They do not go out for pollen or honey, but stay in the hive. They are usually the new bees—i. e., the youngest or most recently added workers. After they act as nurses for a week or so they take their places with the food-gathering workers, and other new bees act as nurses. The nurses feed the young or larval bees at first with a highly nutritious food called bee-jelly, which the nurses make in their stomach, and regurgitate for the larvæ. After the larvæ are two or three days old