. Outlines of zoology. Zoology. 86 PROTOZOA THE SIMPLEST ANIMALS. parts of the food have been absorbed, the undigested residue is got rid of at any point of the protoplasm. One or more contractile vacuoles are visible in the cell-substance. They have an excretory function, and serve to get rid of the finer waste products. Life history.—In favourable nutritive conditions the Amceba grows. At the limit of growth it reproduces by dividing into two. In disadvantageous conditions, such as drought, it may become globular, and, secreting a cell-wall or cyst, lie dormant for a time. The cyst-wall is s
. Outlines of zoology. Zoology. 86 PROTOZOA THE SIMPLEST ANIMALS. parts of the food have been absorbed, the undigested residue is got rid of at any point of the protoplasm. One or more contractile vacuoles are visible in the cell-substance. They have an excretory function, and serve to get rid of the finer waste products. Life history.—In favourable nutritive conditions the Amceba grows. At the limit of growth it reproduces by dividing into two. In disadvantageous conditions, such as drought, it may become globular, and, secreting a cell-wall or cyst, lie dormant for a time. The cyst-wall is said to be chitinoid. With the return of favourable conditions the Amceba revives, and, bursting from the cyst with renewed. Fig. 33.—Life history of Amceba. l. Amceba with pseudopodia; «., nucleus; , contractile vacuole. 2. Division in two. 3. Encystation. 4. Escape of Amceba from its cyst. energy recommences the cell-cycle. The conjugation of two Amoebae has been observed, and spore formation oc- casionally occurs. Second Type—Gregarina. Gregarina, a type of those Sporozoa in which the cell is divided into two regions by a partition. Description.—Various species occur in the intestine of the lobster, cockroach, and other Arthropods. When young they are intracellular parasites, but later they become free in the gut. They feed by absorbing diffusible food stuffs, such as peptones and carbohydrates, from their hosts, and store up glycogen within themselves. In many the size is about one-tenth of an inch. There is a firm cuticle of " protoelastin," which grows inwards so as to divide the. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Thomson, J. Arthur (John Arthur), 1861-1933. Edinburgh, Glasgow and London, H. Frowde and Hodder & Stoughton
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Keywords: ., bookauthorth, bookcentury1800, bookdecade1890, booksubjectzoology
