According to Mr. E. W. Nelson, "the individuals of this species swim always at the surface and in little schools arranged in platoons or abreast. They always swim headed upstream against the current, and feed upon floating matter which the current brings them. A platoon may be seen in regular formation breasting the current, either making slight headway upstream or merely maintaining their station, and on the qui vive for any suitable food the current may bring. Now and then one may be seen to dart forward, seize a floating food particle, and then resume its place in the platoon. And thus they may be observed feeding for long periods. They are almost invariably found in running water well out in the stream, or at least where the current is strongest and where floating matter is most abundant, for it is upon floating matter that they seem chiefly to depend. They are not known to jump out of the water to catch insects flying in the air or resting upon vegetation above the water surface, nor do they seem to feed to any extent upon all small crustaceans or other portions of the plankton beneath the surface. [Illustration: FIG. 154.—Everglade Minnow, _Jordanella floridæ_ Goode & Bean. Everglades of Florida. ] "When alarmed—and they are wary and very easily frightened—they escape by skipping or jumping over the water, 2 or 3 feet at a skip. They rise entirely out of the water, and at a considerable angle, the head pointing upward. In descending the tail strikes the water first and apparently by a sculling motion new impetus is acquired for another leap. This skipping may continue until the school is widely scattered. When a school has become scattered, and after the cause of their fright has disappeared, the individuals soon rejoin each other. First two will join each other and one by one the others will join them until the whole school is together again. Rarely do they attempt to dive or get beneath the surface; when they do they have great difficulty in keeping under and soon come to the surface again." [Illustration: FIG. 155.—Mayfish, _Fundulus majalis_ (L.) (male). Wood's Hole. ] [Illustration: FIG. 156.—Mayfish, _Fundulus majalis_ (female). Wood's Hole. ] [Illustration: FIG. 157.—Top-minnow, _Zygonectes notatus_ (Rafinesque). Eureka Springs, Ark. ] [Illustration: FIG. 158.—Death Valley Fish, _Empetrichthys merriami_ Gilbert. Amargosa Desert, Cal. Family _Pœciliidæ_. (After Gilbert.) ] [Illustration: FIG. 159.—Sword-tail Minnow, male, _Xiphophorus helleri_ Heckel. The anal fin modified as an intromittent organ. Vera Cruz. ]