. The microscope; a simple handbook. Microscopes. Fig. 129.—^Holopedium. there is a history in an abbreviated form of the stages through which the species originally developed. The so-called water- fleas, for instance, are little crustaceans like small shrimps. They are hatched out from eggs as small oval bodies with short legs, and very little else except one eye. After a time the young creature casts ofi its skin and becomes rather more elaborate in form. This goes on stage by stage till it develops into a creature with the most complete series of. legs, antennae, tail, and other appendages.
. The microscope; a simple handbook. Microscopes. Fig. 129.—^Holopedium. there is a history in an abbreviated form of the stages through which the species originally developed. The so-called water- fleas, for instance, are little crustaceans like small shrimps. They are hatched out from eggs as small oval bodies with short legs, and very little else except one eye. After a time the young creature casts ofi its skin and becomes rather more elaborate in form. This goes on stage by stage till it develops into a creature with the most complete series of. legs, antennae, tail, and other appendages. It has as- sumed the appearance of a small shrimp. In some species it goes further, and after having for a short time lived a free and energetic life it develops into nothing but a bag and suckers, which attach themselves to fishes and suck their nutriment from the fish's body. This points to a degeneration in the development which has taken place in the history of a race who found it less fatiguing, if less honourable, to live on other people rather than to fight their own battle in life. These small Crustacea, generally known as water-fleas, are one of the chief foods of fish, both salt and fresh water. They exist in such enormous numbers in some parts that they even satisfy the appetite of the whale. The sea is sometimes of a blood- red colour due to the myriads of a coloured form of these creatures. There is no pond that has not many varieties, and they can be best captured with a collecting net. Certain forms are phos- phorescent, but aU are more or less trans- parent, and can be thoroughly investi- gated under the microscope. Fig. 129 shows one form found in the lakes of Cumberland, which is supposed to be a delicacy beloved by the salmon trout and the char. This curious species is em- bedded in an envelope of jeUy much larger than itself. It is quite transparent. The rolling of its single eye, the beating of its heart, and the digestion of its food, can all be watched
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectmicroscopes, bookyear
