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INDIGESTIBILITY OF THE EGGS OF THE COMMON FROG (Rana temporaria) TO THE COMMON HERON (Ardea c. cinerea) PHILIP M. MILES AN introduction to this article can conveniently be made by includ- ing some details of a revival in September, 1956, of the courtship behaviour of the common frog. After a period of below average temperature during August, 1956, there followed some very warm days in September, when temperatures were well above average, which were accompanied by heavy showers. Several warm showery days and nights elapsed before the frogs became active when a number were seen on the move at night in several places. During the last week of September a frog was seen swimming in a lake of approximately two acres situated at an altitude of about 350 ft. above sea level near Trawscoed, in Cardiganshire, and others were heard croaking in the marsh bordering the shallow western end. Further observations made in October, failed to reveal any coupled frogs or spawn, and no frogs were seen in the water at the end of the month. Herons which frequent this lake had, during the revival of court- ship behaviour in the frogs, eaten some of them. The area below two perches regularly used by herons visiting the lake was in- vestigated in October and several masses of ejecta were found scattered about. These ejecta were examined and found to be of two distinct types, the first (a) having the appearance of irregularly shaped blobs composed entirely of a whitish jelly-like substance apparently derived from the gelatinous glands of the lining of the oviducts of frogs. These blobs were variable in size but on an average two to three times the size of the second type (b), which contained only masses of mucous-covered closely adhering frog eggs. Some of these ejecta were roughly spherical, and variable in size up to approximately three quarters of an inch in diameter. Both forms of ejecta would be most accurately described as fragmentary, in particular type (a), which was found spattered about the foliage and hanging from wire fencing, as well as being scattered on the ground up to a radius of three feet from the perches. No ejecta were found which contained a mixture of the two sub- stances, i.e., Whitish jelly-like (albuminous) material and eggs or any other kind of indigestible remains At the lake referred to, during the normal breeding season of the frogs, a considerable number are eaten by herons and at that time the grassy banks where the frogs have been killed are strewn with frog spawn. In this case the eggs are surrounded by their protective covering of jelly and have obviously been shed by the frogs under the stress of having been seized and almost certainly injured by the herons. It would be interesting to discover if the