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Passing by the simple vital processes of the monera, or single-celled "things," we notice the higher forms of cell life, with growing sensibility or sensation. Then we come to the cell-groups, in which the individual cells manifest sensation of a kind, coupled with a community-sensation. Food is distinguished, selected and captured, and movements exercised in pursuit of the same.
In the case of certain plants and animals, cell-groups grow together into a so-called "bud," which later detaches itself from the parent body and forms a new individual living organism, as in the case of the polyps or the tubers in plant life. A tree, for instance, may be grown from a graft which has been cut off and planted in the ground.
As the two parts separate, the protoplasm of each groups itself around its nucleus, and two living forms exist where there was but one a moment before. And then each of the two cells proceed to grow rapidly, and then separate, and so on to the end, each cell multiplying into millions, as time passes. Ascending in the scale, we next find the living forms composed of cell-groups.
These cell-groups are formed by single cells dividing, and then subdividing, but instead of passing on their way they group themselves in clusters, or masses. There are millions of forms of these cell-group creatures, among which we find the sponges, polyps, etc.
Under this is a soft medullary substance, which consists of entodermic cells with vacuoles. These gonads are not yet independent sexual glands, but sexually differentiated cell-groups in the medullary substance, or, in other words, parts of the gut-wall. Most of the Platodaria have not the muscular pharynx, which is very advanced in the Turbellaria and Trematoda.
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