Page:VCH Warwickshire 1.djvu/214

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A HISTORY OF WARWICKSHIRE Claus maintains that at least the little bleak and the minnow are as ready to feed on the Argulus as the Argulus is to feed on them. Claus is will- ing to retain the term Branchiura for this group, although objecting that the tail is not in fact more branchial than some other parts of the body. It is, indeed, he says, the seat of an extraordinarily rich and lively blood circulation, and by its muscular arrangement is adapted for rhythmical contractions and expansions, so that its function is that of an auxiliary heart. 1 In contrast with the foregoing very limited set of forms, the Clado- cera, which constitute the remaining section of the Branchiopoda, are a group of remarkable extent and importance in the fresh waters of the world. Though in almost all species the individuals are small, and in many descend to microscopic minuteness, they make amends for this by their prodigious fertility. Like the aphides that infest our roses and other plants, these entomostracans multiply by parthenogenesis. Milton represents Adam as lamenting that the Creator did not ' fill the world at once with men, as angels, without feminine.' Parthenogenesis is a device for filling it ' without masculine,' and setting up a republic of amazons. Nevertheless there come periods when it seems to be borne in upon the minds of these self-sufficient females that nature is not completely satis- fied with their procedure. They then form what are known as the ' resting eggs,' which require to be fertilized by the male before they are detached from the mother. They are then capable of ' resting ' for long periods in mud, which may become thoroughly dry. When at a suitable season water comes again to the soil the buried entomostracans hatch out and a new cycle begins. In 1895 Mr. T. V. Hodgson, now engaged as naturalist on board the antarctic exploring vessel, the Discovery, published a 'Synopsis of the British Cladocera.' To this he appended a list containing all those species which had up to that time been recorded from the neighbourhood of Birmingham, 'a region which may be defined as being within a fifteen mile radius.' 2 Mr. Hodgson has since informed me that as a matter of fact all the species mentioned in the list have occurred in Warwickshire. The question was raised, because localities are not in every case specified, and a fifteen mile radius round Birmingham includes a district obviously not conterminous with the county. The catalogue comprises twenty- nine species and two varieties. Although these are far less than half the number of British Cladocera now known, they involve almost all the chief outlines of the existing classification. In the same year (1895) D r - Jules Richard began his excellent Revision des Cladoceres with the following definition of this group : ' Entomostraca free, minute. Head distinct. Rest of the body as a rule laterally compressed and covered by a bivalved test. Second antennas 1 Zeitichrift fur wissenschaftfiche Zoo&gie, xxv. 269 (1875). 8 Journal of the Birmingham Natural History and Philosophical Society, vol. i. No. 19, pp. 101-112 (February, 1895). It will be understood that subsequent quotations, where not otherwise indicated, refer to this paper. I 7 6