Elementary biology; an introduction to Elementary biology; an introduction to the science of life elementarybiolog00grue Year: 1924 SOCIAL LIFE OF ORGANISMS 431 for its sustenance. But among these higher algae the growth of the mass of cells assumes a rather definite form, and certain of the groups of cells become specialized as anchorage organs, others become specialized as reproductive organs, and so on ; and it takes all of these together to make up a complete life. Fig. 228. Colony of Hydractinia In this colonial animal (related to the jellyfish and to corals), as in many others, there
Elementary biology; an introduction to Elementary biology; an introduction to the science of life elementarybiolog00grue Year: 1924 SOCIAL LIFE OF ORGANISMS 431 for its sustenance. But among these higher algae the growth of the mass of cells assumes a rather definite form, and certain of the groups of cells become specialized as anchorage organs, others become specialized as reproductive organs, and so on ; and it takes all of these together to make up a complete life. Fig. 228. Colony of Hydractinia In this colonial animal (related to the jellyfish and to corals), as in many others, there are distinct kinds of individuals, called hydranths. a, vegetative, or food-getting, hydranths, which take in and digest food for the whole colony; 6, vegetative hydranths in various stages of contraction ; c, protective, or fighting, hydranths, which bear large numbers of nettling cells ; d, reproductive hydranths, male and female, which throw off sperm cells and egg cells respectively ; e, buds, or undeveloped hydranths. (Photograph from model in American Museum of Natural History) If we consider the whole plant as an individual, we see that it is quite possible for a single plant to continue its life without relation to any others of the species. In general this is true of all the plants, from the lowest to the highest. 458. Differentiated cells. When we pass from the one-celled animals to the sponges (Fig. 227), we find that while the life
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