Changes in body-length, and in shape of the furcal ramus, of a freshwater cyclopoid copepod

Some morphological relationships during larval development of a freshwater cyclopoid copepod (Crustacea), Cyclops strenuus abyssorum Sars (Gurney, 1933) have been studied. The proportion which the cephalothorax forms of total length decreases at each copepodid moult whilst that which the furcal ramus forms increases. However, within each instar, each of these ratios is a constant at different seasons and in different lakes. The amount by which total length in one instar is greater than that in the preceding instar tends to decrease at each moult from a maximum of 1.31 in the first copepodid moult to lower values, especially in males. The furcal ramus is twice as long as wide in the first copepodid instar but seven times as long as wide in the adult female. This change is enhanced in the last two moults not only by a proportionately greater increase in length over width but by an absolute reduction in width itself.