Feeding.

The food of the early instars of S. Prasina consists of diatoms and algae, as in other genera of stone-flies. The particular diatom fed upon by a nymph taken from the Temuka River was a species of Navicula, together with filaments of algae. Of the first instars hatched in captivity only one endeavoured to feed when placed in a culture of Protozoa, Rotifers, Tardigrada, Algae, Elodea, and Nitella. This individual ate three Rotifers, which caused it great discomfort; it died shortly afterwards. The milling action of the gizzard could be clearly seen. At each peristalsis a vigorous contraction occurred in the gizzard, compressing the food until it was masticated; then, and not before, was it allowed to pass into the mesenteron. Evidently the enzymes present at this stage were not capable of acting upon a carnivorous diet, for the Rotifers in question passed unaltered right through to the rectum, in which region they were lodged when the insect died. In spite of the change from a herbivorous diet in these early instars to a carnivorous one in later, the mouth-parts are of the typical biting type throughout.

Bibliography.

Helson, G. A. H., 1934. Bionomics and Anatomy of Stenoperla prasina, Trans. Roy. Soc. N.Z., vol. 64, pp. 214–248.

Imhoff, L., 1881. Beitr. zur Anat, von Perla maxima, Inaug. Diss. Aara.

Imms A. D., 1925. A Textbook of Entomology, first edition. Methuen and Co., Ltd., London.

Percival. E., and Whitehead, H., 1928. Observations on the Ova and Oviposition of Certain Ephemeroptera and Plecoptera, Proc. Leeds Phil. Soc., vol. 1, pp, 271–288.

Przibram, H., 1931. Connecting Laws in Animal Morphology, Univ. Lond. Press, London.

Rosseau, E., Lestage, J., and Schouteden, H., 1921. Les Larves et Nymphes Aquatiques des Insectes d'Europe, vol. 1, Office de Publicite, Brussels.

Samal. J., 1923. Etudes morph. et biol. de Perla abdominalis, Ann. de Biol. Lac. 12.

Wigglesworth, V. B., and Sikes, E. K., 1931. The Hatching of Insects from the Egg and the First Appearance of Air in the Tracheal System, Q.J.M.S., vol. 74, pp. 165–192.