. Outlines of zoology. Zoology. r, 2. — Structure of the cell. (After Carxoy.) Nucleus with chro- matic coil, note proto- plasmic reticulum. Within the nucleolus an " endo-nucleolus " has been dis- covered. Though the nuclei of different cells differ in details, there is a fundamental sameness, both of structure and activity, throughout the world of cells. ((-) TAe Cetitrosomes.—When a cell divides into two, the chromatin elements or chromosomes of the nucleus are also divided and separate to form the two daughter nuclei. In this separation extremely fine " archoplasmic " t
. Outlines of zoology. Zoology. r, 2. — Structure of the cell. (After Carxoy.) Nucleus with chro- matic coil, note proto- plasmic reticulum. Within the nucleolus an " endo-nucleolus " has been dis- covered. Though the nuclei of different cells differ in details, there is a fundamental sameness, both of structure and activity, throughout the world of cells. ((-) TAe Cetitrosomes.—When a cell divides into two, the chromatin elements or chromosomes of the nucleus are also divided and separate to form the two daughter nuclei. In this separation extremely fine " archoplasmic " threads have been seen passing to the chromo- somes from beside two minute bodies in the cytoplasm. These two bodies are called central corpuscles or centro- somata (Figs. 3 and 4); they seem to act like two centres of force. They also occur, in most cases singly, in resting cells, and it seems likely that they are constant parts of the cell, and that they arise from within the nucleus. (d) The Cell Wall.—To the earlier histologists, who often spoke of cells as little bags or boxes, the wall seemed of much moment. It is, however, the least important part of the cell. In plant cells there is usually a very distinct wall, consisting of cellulose. This is a product, not a part, of the protoplasm, though some protoplasm may be intimately associated with it as long as its growth continues. In animal cells there is rarely a very distinct wall chemically distinguish- able from the living matter itself. J3ut the maigin is often different from the interior, and a slight wall may be formed by a superficial compacting of the threads of the cell network, or by a physical alteration of the cell substance, comparable to the forma- tion of a skin on cooling porridge. In other cases, especially in cells active, such as ova and encysted chr. Fig. 3.—Fertilised ovum of Ascaris. (After BOVERI.) chr. Chromatin elements, two from ovum nucleus and two from sperm nucleus; cs. centrosoma from^^
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
