The Long Island Cyclops (C. insignis?), having fourteen-jointed antennae, three-jointed rami in the swimming feet, with two-jointed fifth feet and elongate caudal stylets, is a transitional stage in the development of a seventeen-jointed form C. parcus (Herrick ?). The eighteen-jointed antenna is derived from the seventeen-jointed form by division of the seventh segment.Out of fifteen individuals taken at random, none of whose antennal segments exceed twelve, five precisely similar individuals constitute a group having nine antennal segments, two-jointed rami and two-jointed fifth feet.Four individuals constitute a second group having typically ten antennal segments, two-jointed rami, and two-jointed fifth feet. Two of these individuals show marked variation, one in having three-jointed rami in the swimming feet, the other in having a one-jointed fifth foot.Four individuals constitute a third group, characterized by eleven-jointed antennae, three-jointed rami, and two-jointed fifth feet. One member of this ...