Ctenophorae (comb-or fringe-bearers; Gr. gen. a comb, and to bear), the beroid medusae, the highest order of the class of acalephs or jelly fishes. They are more or less spherical, the body being made up of eight homologous segments, bearing eight rows of locomotive appendages. About 70 species are enumerated by Agassiz, distributed in more than 30 genera. Of the pleurobrachia, common on the N. E. coast of America, he says: "When active, it hangs out a pair of most remarkable appendages, the structure and length and contractility of which are equally surprising, and exceed in wonderful adaptation all I have ever known among animal structures. Two apparently simple, irregular, and unequal threads hang out from opposite sides of the sphere. Presently these appendages may elongate, and equal in length the diameter of the sphere, or surpass it, and increase to 2, 3, 5, 10, and 20 times the diameter of the body, and more and more; so much so, that it would seem as if these threads had the power of endless extension and development.

But, as they lengthen, they appear more complicated; from one of their sides other delicate threads shoot out like fringes, forming a row of beards like those of the most elegant ostrich feather, and each of these threads itself elongates till it equals in length the diameter of the whole body, and bends in the most graceful curves." A common species of idyia, of our coast, of a beautiful rose color, attaining a length of three or four inches, is sometimes so abundant in summer as to tinge large patches of the sea with a delicate rosy hue. They are all voracious, feeding on their fellows.

Pleurobrachia.