1911 Encyclopædia Britannica/Siren

SIREN, a name derived from the Greek Sirens (see below) for an acoustical signalling instrument specially used in lighthouses, &c. (see Lighthouse), and applied by analogy to certain other forms of whistle. In zoology the siren (Siren lacertina), or “mud-eel” of the Americans, one of the perennibranchiate tailed batrachians, is the type of the family Sirenidae, chiefly distinguished from the Proteidae by the structure of the jaws, which, instead of being beset with small teeth, are covered by a horny sheath like a beak; there are, however, rasp-like teeth on the palate, and a few on the inner side of the lower jaw, inserted on the splenial bone. The body is eel-like, black or blackish, and only the fore-limbs are present, but are feeble and furnished with four fingers. It grows to a length of three feet and inhabits marshes in North and South Carolina, Florida and Texas. A second closely-allied genus of this family is Pseudobranchus, differing in having a single branchial aperture on each side instead of three, and only three fingers. The only species, P. striatus, is a much smaller creature, growing to six inches only, and striated black and yellow; it inhabits Georgia and Florida.

As E. D. Cope has first shown, the siren must be regarded as a degenerate rather than a primitive type. He has observed that in young specimens of Siren lacertina (the larva is still unknown) the gills are rudimentary and functionless, and that it is only in large adult specimens that they are fully developed in structure and function; he therefore concludes that the sirens are the descendants of a terrestrial type of batrachians, which passed through a metamorphosis like the other members of their class, but that more recently they have adopted a permanently aquatic life, and have resumed their branchiae by reversion. From what we have said above about Proteus and similar forms, it is evident that the “perennibranchiates” do not constitute a natural group.

See E. D. Cope, “Batrachia of North America,” Bull. U.S. Nat. Mus. No. 34 (1889), p. 223.