The Hypanis, a river of Pontus, brings down in its waters, about the time of the summer solstice, small membranous particles, like a grape-stone in appearance; from which there issues an animal157 with four legs and with wings, similar to the one just mentioned. It does not, however, live more than a single day, from which circumstance it has obtained the name of “hemerobion.”158 The life of other insects of a similar nature is regulated from its beginning to its end by multiples of seven. Thrice seven days is the duration of the life of the gnat and of the maggot, while those that are viviparous live four times seven days, and their various changes and transformations take place in periods of three or four days. The other insects of this kind that are winged, generally die in the autumn, the gad-fly becoming quite blind159 even before it dies. Flies which have been drowned in water, if they are covered with ashes,160 will return to life.