The name "Cirripedes" is commonly used for the order or group formed by the barnacles—in allusion to the plume-like appearance of their "raking" legs. Stalked barnacles often are found in the ocean attached to floating pumice-stone, and one species has been discovered attached to the web of the foot of a sea-bird. They, like many other creatures, benefit by being carried far and wide by floating objects. Whales have very large and solid acorn-barnacles peculiar to them, fixed deeply in their skin. Others attach themselves to marine turtles.

With few exceptions the crustaceans are of separate sexes, male and female. But in nearly all classes of animals we find some kinds, even whole orders, in which the ovaries and spermaries are present in one and the same individual. "Monœcious" or "one-housed"—that is to say, possessing one house or individual for both ovaries and spermaries—is the proper word for this condition, but a usual term for it is "hermaphrodite." "Diœcious" is the term applied to animals or plants in which there are two kinds of individuals—one to carry the spermaries, the male, and the other to carry the ovaries, the female. It is probable that the monœcious condition has preceded the diœcious in all but unicellular animals. In vertebrate animals as high as the frogs and the toads we find rudimentary ovaries in the male, and in individual cases both ovaries and spermaries are well developed. Such a condition is not rare as an individual abnormality in fishes. In some common species of sea-perch (Serranus) and others it is not an exception but the rule.

Many groups of molluscs are monœcious, and it is not in any way astonishing to find a group of crustaceans which are so. The Cirripedes or barnacles are an example. It is probable that the presence of ovaries and spermaries in the same individual—the monœcious condition—is an advantage to immovable fixed animals. During the voyage of the "Beagle," and making use on his return of the collections then obtained, Darwin carried out a very thorough study of the Cirripedes of all kinds from all parts of the world. He worked out their anatomy minutely, classified the 300 different kinds then known, and described many new kinds. The stalked barnacles often occur in groups, the individuals being of different ages and sizes, the small young ones sometimes fixing themselves by their sucker-bearing heads to the stalks of their well-grown relatives. In all the varied kinds studied by Darwin he found that the full-grown individuals were monœcious—that is, of combined sex—as was known to be the case in those studied before his day. But Darwin made the remarkable discovery that in two kinds of stalked barnacles (not the common ship's barnacles), comprising several species, "dwarf males" were present perched upon the edge of the shell of the large monœcious (bi-sexual) individuals. These dwarf males were from one-tenth to one-twentieth the length of the large normal monœcious individuals, but usually possessed the characteristic details of the shell-valves and other features of the latter.

This existence of a sort of supernumerary diminutive kind of male as an accompaniment to a race of normal monœcious individuals was quite a new thing when Darwin discovered it. That all the males in some diœcious animals are minute as compared with the females was known, and has been established in the case of some parasitic crustaceans, in some of the wheel-animalcules, and in the most exaggerated degree in the curious worms, Bonellia and Hamingia. But the existence of "complemental males," as Darwin called them, existing apparently in order to fertilize the eggs should they escape fertilization by the ordinary monœcious individuals, was a new thing. And it was doubted and disputed when Darwin described his observations fifty-six years ago. They were, in fact, by many regarded as a distinct species parasitic upon the larger barnacles on which they were found until Darwin's conclusion as to their nature was confirmed by the report of Dr. Hoek, on the barnacles brought home by the "Challenger" expedition.

It is an interesting fact that recent studies have shown that in some of the barnacles with dwarf males (species of Scalpellum) the large individuals are no longer monœcious, but have become purely females, whilst in some other species dwarf males have been discovered which have rudimentary ovaries. Thus we get gradations leading from one extreme case to the other. Darwin always felt confidence in his original observations on this matter, and was proportionately delighted when, after thirty years, his early work was proved to be sound. In the Natural History Museum at the Darwin centenary in 1909, a temporary exhibition of specimens, note-books, and letters associated with Darwin's work, was brought together. His original specimens and drawings of Cirripedes and of the wonderful little "complemental males" of the barnacles were placed on view.

CHAPTER XIV
THE HISTORY OF THE BARNACLE AND THE
GOOSE

THE curious belief, widely spread in former ages—that the creatures (described in the last chapter) called "barnacles" or "ship's barnacles"—often found attached in groups to pieces of floating timber in the sea as well as fixed to the bottoms of wooden ships—are the young of a particular kind of goose called "the barnacle goose," which is supposed to hatch out of the white shell of the long-stalked barnacle, is a very remarkable example of the persistence of a tradition which is entirely fanciful. It was current in Western Europe for six or seven centuries, and was discussed, refuted, and again attested by eminent authorities even as late as the foundation of the Royal Society—the first president of which, Sir Robert Moray, read a paper at one of the earliest meetings of the society in 1661, in which he described the bird-like creature which he had observed within the shell of the common ship's barnacle, and favoured the belief that a bird was really in this way produced by a metamorphosis of the barnacle.

The story was ridiculed and rejected by no less a philosopher than Roger Bacon in the thirteenth century, and was also discredited by the learned Aristotelian Albertus Magnus at about the same time. No trace of it is to be found in Aristotle or Herodotus or any classical author, nor in the "Physiologus." The legend seems to have originated in the East, for the earliest written statement which we have concerning it is by a certain Father Damien, in the eleventh century, who simply declares: "Birds can be produced by trees, as happens in the island of Thilon in India." We have also a reference to the same marvel in an ancient Oriental book (the "Zohar," the principal book of the Kaballah), as follows: "The Rabbi Abba saw a tree from the fruits of which birds were hatched." The earliest written statements of the legend are, it appears, to the effect that there is a tree which produces fruits from which birds are hatched. The belief in the story seems to have died out at the end of the seventeenth century, when the structure of the barnacle lying within its shell was examined without prejudice, and it was seen to have only the most remote resemblance to a bird. The plumose legs or "cirrhi" of the barnacle (Fig. 10) have a superficial resemblance to a young feather or possibly to the jointed toes of a young bird, and there the possibilities of comparison end.