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. 



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