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Updated: May 24, 2025
Without leaving the group of one-celled animals typified by Amoeba, we find colonies of the most elementary biological nature, where other natural obligations are added to the two of greatest importance. Some species of the bell-animalcule, Vorticella, provide characteristic examples of these primitive compound protozoa.
Suppose we could go further than is now possible and could lay bare the ultimate make-up of the chromatin of these one-celled creatures, would we even then be able to prove that life with all its properties is inherent in these material components of the cells? In other words, would we really solve anything after all?
The earliest one-celled protozoa were probably succeeded by many- celled animals of the type of the blastosphere, and these by gastrula-like organisms. From the gastrula type the higher sub- divisions of animal life probably diverged, as separate branches from a common trunk.
Larie was all alone in a little world. He had lived there many days, and had spent the time, minute by minute and hour by hour, doing nothing at all but growing. That one thing he had done well. There is no doubt about that; for he had grown from a one-celled little beginning of life into a creature so big that he filled the whole of his world crammed full.
These differences are due to the fact that the stuff is alive, and within it are constantly going on those changes accompanying metabolism, or the building up and tearing down processes that always accompany life. All separate masses of protoplasm, such as the one-celled amoeba or the individual cells of our own bodies, are constantly taking in food and as constantly throwing off wastes.
How do the cells enable the body to grow? Describe the process of cell-division. How does the general work of cells differ from their special work? Define absorption, excretion, and assimilation as applied to the cells. Compare the conditions surrounding a one-celled animal, living in water, to the conditions surrounding the cells in the body.
There must be permanent pores in the membrane to receive food or let out rays of the living substance to act as oars or arms. Thus we get an immense variety amongst these Protozoa, as the one-celled animals are called. Some have a definite mouth-funnel, but no stomach, and cilia drawing the water into it.
Were the statement iterated and reiterated on every page and in every paragraph, there would be no undue emphasis put upon the astounding fact that the apparently impassable gap between a one-celled animal like Amoeba and a mammal like a cat is actually compassed during the development of the last-named organisms from single cells.
Let us begin with the Protozoa, or one-celled forms the lowest form of animal life. The lowest form of this lowest class is that remarkable creature that we have mentioned in previous lessons the Moneron. This creature lives in water, the natural element in which organic life is believed to have had its beginning.
The clearest evidences as to the stages in the evolution of sexual reproduction is found in the plant world among the green algæ. In the lower orders of one-celled algæ, reproduction takes place by simple cell division. In some families, this simple division results in the production of several new individuals instead of only two from each parent cell.
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