MINUTE TUINGS OF LIFK. 1G9 



exigencies of popular English. Tlio watcr-flcas {DapJnu'a and its 

 allies) are very pretty little tilings — something like etherializecl 

 shrimps in delicate transhicent bivalve shells or carapaces folded 

 down on each side, and inclosing all the animal except its feathery 

 ontennfc or swimming organs. It is more scientific to say that the 

 two lialves of the carapace of the shrimp would rejn'csent the two 

 halves of the little shell, which is very much extended, backwards 

 and downwards on each side, inclosing the inturncd hinder parts 

 of the animal, with the limbs modified in character and number ; 

 and instead of long thin thread-like feelers in front, the creature 

 has two pairs of modified antenna?, filamentous, beautifully jointed, 

 and so arranged that with them the animals can either swim in 

 the water or creep along on the mud and weeds. These antennae 

 protrude and work through a notch in the edge of the shell, just 

 below the head, which is thus made to look like a kind of pro- 

 jecting hood. Though small, yet the Daphnm occur in such 

 enormous numbers that at one season of the year, when they take 

 a red colour, they sometimes give a bloody appearance to ponds of 

 water, and before now this has been taken for a prognostic of bad 

 times ; but it is only when bred under favourable circumstances 

 in such myriads that they crowd the water and colour it until one 

 generation dies away and gives place to others. 



IN^one of these add to the rock-material, because they are of soft 

 tissue, slightly horny at most. The Ostracoda are a different kind 

 of Entomostraca. They have hardish bivalve shells, which remain 

 often in the fossil state. The Ctjpris and Candona live in fresh water, 

 and have somewhat egg-shaped valves, which open wide enough to 

 allow the two pairs of autennte to come out and move in front, and the 

 hooked tail to be pushed outwards and downwards behind. Cypris 

 has feathered antennae or front limbs and can swim ; in Candona the 

 lower antennse are merely hooked, so that this animal can only 

 crawl on the mud and weeds. The Cytliere is marine, and does not 

 swim, but crawls about. It differs from the foregoing in some of its 

 limbs and in having stronger valves, thicker, and hinged along the 

 back. They are like little peach-stones in some cases, and much 

 more oblong in others; and nearly always ornamented on the surface. 

 These creatures have added very considerably to the world's crust, 

 little as they are. They may very readily be found living ; they 

 thrive in aquariums ; they are easily collected from among the 

 water- weeds of ponds. The mud thrown out of the river at the silk- 

 mills, near Watford, some years ago, was grey with the little white 

 specks of the dead valves. In the fossil state these Entomostraca are 

 very abundant ; Cythere and its allies in marine strata ; Cypridce 

 in lacustrine beds. In the Silurian rocks there are many marine 

 forms ; and in the Devonian schists they lie very thick, but much 

 squeezed and distorted. In the Carboniferous formation they are 

 also abundant ; some, in the Coal-measures, are estuarine. Here is a 

 piece of Tertiary rock from Eombay; the little black spots in it are 

 all Cypridce. Here is a piece of similar limestone converted into 

 flint, and each of these little creatures is represented by a lovely 



