In New York State, every swift stream which has a bed of gravel and flat stones ought to contain some one of the Johnny darters, for there are a great many different kinds (Fig. 85). They are little creatures, delighting in clear water and swift currents where they dart about, hiding under stones and leaves, or resting on the bottom with their heads up-stream. The body of a darter is compact and spindle-shaped, gradually tapering from the short head to a narrow tail. The eyes are situated nearly on top of the head. The color of the darters varies greatly with the different kinds. Some are very plain, the light ground color being broken only by a few brown markings. Others are gorgeous in their colorings, it seeming as if they had attempted to reproduce the rainbow on their sides. Such kinds are indeed very attractive and are ranked with the most beautifully colored of all our common fishes. When a darter swims, he appears bird-like, for he flies through the water much as a bird flies through the air. He does not use his tail alone in swimming, as the catfish, the sunfish, the stickleback, and most of the other fishes do, but flies with his pectoral fins. [Illustration: _Fig. 85. A Johnny Darter._] You surely must have a Johnny darter in your aquarium jar. The Johnnies are true American fishes. Though small, they face the strong currents and eke out a living where their larger cousin, the yellow perch, would perish. There are many interesting facts which may be learned from the Johnny darters when kept alive in an aquarium. When not actually moving in the water, do the Johnnies rest on the bottom of the jar or remain suspended in the middle apparently resting on nothing, as the other aquarium fishes do? When a fish remains still in the middle of the jar he does so because he has a well-developed air-bladder to help buoy him up, and when a fish dies it is the air-bladder which causes him to turn over and rise to the top. Now if the Johnnies always rest on the bottom of the jar when not swimming and if one happens to die and does not rise to the top we may know that, if he has an air-bladder at all, it is only a vestigial one. It would be interesting also to find out for ourselves whether a Johnny darter can really "climb trees" (I mean by trees, of course, the water plants in the aquarium jar), or if he can perch upon the branches like a bird. THE MINNOWS. [Illustration: _Fig. 86. A convenient form of aquarium jar supplied with water plants. The bottom is covered with clean sand and flat stones._]