The natural history of the British Entomostraca, Volume 13 (Google eBook)

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The Ray society, 1850 - 364 pagine
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Pagina 78 - The myriads necessary to produce this effect are really astonishing, and it is extremely interesting to watch their motions. On a sunshiny day, in a large pond, a streak of red, a foot broad, and ten or twelve yards in length, will suddenly appear in a particular spot, and this belt may be seen rapidly changing its position, and in a very short time wheel completely round the pond. Should the mass come near enough the edge to allow the shadow of the observer to fall upon them, or should a dark cloud...
Pagina 333 - The sailors imagine this Shark is blind, because it pays not the least attention to the presence of a man ; and is, indeed, so apparently stupid, that it never draws back when a blow is aimed at it with a knife or lance.
Pagina 5 - is at hand, when the causes of disease shall not only be sought after in the air, in our method of living, &c., but in the incautious use of waters often abounding in innumerable animalcules.
Pagina 79 - On a sunshiny day, in a large pond, a streak of red, a foot broad, and ten or twelve yards in length, will suddenly appear in a particular spot, and this belt may be seen rapidly changing its position, and in a very short time wheel completely round the pond. Should the mass come near enough the edge to allow the shadow of the observer to fall upon them, or should a dark cloud suddenly obscure the sun, the whole body immediately disappear, rising to the surface again when they have reached beyond...
Pagina 67 - By numerous filaments which it darts forth, he says, it causes such motion in the water as to attract unresistingly the insects in the water to its mouth. " Thus it exists," he concludes, " a life of rapine and destruction, enjoyed at the expence of the lives of thousands ; and as the objects of its ravenous disposition are defenceless, so are they the sport of their conqueror ; the few moments of intermission its craving appetite grants them, is occupied equally in the spoil, first pressing them...
Pagina 189 - Cyclops quadricornis in particular, and has given a calculation which shows the amazing fertility of the species. He has seen one female isolated lay ten times successively ; but in order to speak within bounds he supposes her to lay eight times within three months, and each time only forty eggs. At the end of one year, this female would have been the progenitor of 4,442,189,120 young!! The first mother lays forty eggs, which at the end of three months, at eight layings during that time, would give...
Pagina 6 - ... see a decided fitness in these Entomostraca being carnivorous, thus helping to prevent the noxious effects of putrid air which might otherwise ensue ; whilst they in their turn become a prey to other animals, which no doubt serve their purposes also in the economy of nature.
Pagina 4 - As this may be considered/me of the benefits conferred by these insects, it may be useful to know the evils to man they may be likely to produce. " Though they are most abundant in stagnant water, they yet occur in considerable numbers in the purer sorts of water that serve as our common drink, and may frequently...
Pagina 151 - ... they" to use the words of Miiller, " by opening their valves, enjoy light, and move at their will, sometimes burying themselves in the mud, sometimes darting through the water, the humid air of their sphere. If they meet any unforeseen object, they conceal themselves all at once in their shells and shut the valves, so that force and address seek in vain to open them.
Pagina 6 - Entomostraca will then be seen speedily to assume another aspect. They become lively and active, and the opacity of their alimentary canal testifies sufficiently the cause of it. When, indeed, we consider the amazing quantity of animals which swarm in our ponds and ditches, and the deterioration of the surrounding atmosphere which might ensue from the putrefaction of their dead bodies, we see a decided fitness in these...

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