The sex classes and age classes of various species of ducks constitute measurable elements of the populations. The present study deals primarily with sex ratios and age ratios and the ways in which they relate to population productivity. The present study is an evaluation of sex and age ratios in North American duck populations and the ways in which, in waterfowl management, these ratios can be used to measure productivity. Drakes occurred in relatively greater numbers among diving ducks than among dabblers; however, examination of the available knowledge on the reproductive biology characterizing these two subfamilies revealed nothing which suggests that extra drakes may be more important to the maintenance of populations of diving ducks than of dabblers. Juveniles were found to be more vulnerable to hunting than adults; the vulnerability differential varied with place, time of hunting season, vear, and species. Age ratios obtained from bagged ducks and corrected for the greater vulnerability of juveniles offered the best means of determining the adult-juvenile composition of duck populations.

* I am not quite sure whether uiy own name or that of Sars should have precedence, as I know not the exact date of Sara's paper. (J. serratus was described by me at the Brit. Assoc. Meeting of 1861, the same year as that of the paper of Sars. A. M. N. 1() MACRURA.

No abstract

There is no heart in Lepeophtlieirus, nor are there any proper blood-vessels. The circulation is wholly laounar. The bloodstreams simply pass through the spaces left among the internal organs and between the connective-tissue bands of the body-wall. The streams appear to have certain definite courses, but they are not uniform, continuous currents. The fluid progresses by successive jerks, due to the peristaltic movements of the alimentary canal. The blood is a clear fluid containing numerous colourless corpuscles which vary in size and shape. The corpuscles are able to accommodate themselves to the diameter of the spaces through w T hich they pass. There are no independent organs of respiration, unless the pore-canals and glands in the basal joint of the protopodite of the second and third pairs of feet act as such. Hartog* and others have suggested that the blood is probably aerated from the seawater contained in the alimentary canal by the method of " anal respiration." Further precise observations are, however, required to substantiate this hypothesis, as the method is so entirely different from that in the higher Crustacea. MUSCULAR SYSTEM.

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