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CRUSTACEANS 1785 he described and figured apparently the same form as Daphnia sima. Other closely allied species have since been discovered. Now therefore it is uncertain which of them all was the one originally observed by Miiller. Since Schoedler has incorporated the word sima into the name of the genus, it has been by pretty general consent thought best to follow him in accepting the name vefu/us for the species to which he has given a fairly satisfactory definition under that title. The study of these little ' water-fleas ' is to some extent complicated not only by the difference in shape between male and female, but by the fact that the ' vernal ' female is not quite like the * autumnal ' or ' ephippial ' female. This difference is connected with the phenomena of reproduction. In the earlier stage the female bears numerous eggs which are independent of fertilization, and from which the young ones leave their mother ready for lively existence in their aquatic birthplace. At the later season the mother produces a single egg, which requires to be fertilized, and which is enclosed in a portion of her carapace known as the ephippium. In due course this envelope with the egg inside it is cast off. One could imagine the package labelled in bold handwriting, ' Not to be opened until the recurrence of a season and circumstances favourable to Daphnid life.' At any rate, we find in practice that when the basin of a dried-up pond is again filled with water, the ' resting ' eggs of Daphnia or Simocephalus or any kindred genus are speedily responsive to the voice of nature. They abstain from developing while the surroundings would be fatal, but with the least possible delay emerge into a friendly environ- ment. Lilljeborg, in his great work on the Cladocera of Sweden, says that S. vetulus is one of the most frequent Swedish Cladocera, occurring not only in pools but in marshes and at the sides of greater waters such as rivers and lakes, though always among plants. He notes that the male is found sometimes as early as in July, but most often in September and October. As might be expected, it is during the same months that the ephippial females are usually met with. 1 That Mr. Scourfield at Maidenhead met with the males in May is worth noting as a sign that the seasonal habits of this widely distributed species will not necessarily be the same in all parts of its range. A prophetic eye may discern that the carcinology of Berkshire, which is for the moment in its resting stage, will in the future find a favourable epoch for a full and vivacious development. 1 Cladocera Suecitt (1901), p. 173. 13*