Among the most beautiful of the Siphonophores, is the well-known Physalia or Portuguese man-of-war, represented in Fig. 117. The float above is a sort of crested sac or bladder, while the long streamers below consist of a number of individuals corresponding in their nature and functions to those composing a Hydroid community. Among them are the fertile and sterile Hydræ (Fig. 118), the feeders and Medusæ bells (Fig. 119). The Physalia properly belongs to tropical waters, but sometimes floats northward, in the warm current of the Gulf Stream, and is stranded on Cape Cod. When found so far from their home, however, they have usually lost much of their vividness of color; to judge of their beauty one should see them in the Gulf of Mexico, sailing along with their brilliant float fully expanded, their crest raised, and their long tentacles trailing after them. [Illustration: Fig. 118. Bunch of Hydræ; _a_ base of attachment, _b_ _b_ _b_ single Hydræ, _c_ _c_ tentacles. (_Agassiz_.)] [Illustration: Fig. 119. Bunch of Hydræ; cluster of Medusæ; _b_ _b_ Hydræ with tentacles, _c_ _d_ bunches of Medusæ (_Agassiz_.)] _Velella_. (_Velella mutica_ BOSC.) Another very beautiful floating Hydroid, occasionally caught in our waters, though its home is also far to the south, is the Velella (Fig. 120). It is bright blue in color, and in form not unlike a little flat boat with an upright sail. Its Medusa (Fig. 121) resembles so much that of some of our Tubularians, that it has actually been removed on this account from the old group of Siphonophoræ, and placed next the Tubularians; another evidence of the close affinity between the former and the Hydroids. [Illustration: Fig. 120. Velella; _m_ so-called mouth, _a_ tentacles. (_Agassiz_.)] [Illustration: Fig. 121. Free Medusa of Velella; _a_ proboscis, _b_ chymiferous tube, _c_ circular tube. (_Agassiz_.)] MODE OF CATCHING JELLY-FISHES.