Outlines of zoology . the cell lies the usually single nucleus. The food consistsof minute Algse, such as diatoms, or of vegetable is reason also to suspect cannibalism. The foodis surrounded by the finger-like processes, and engulfed 90 PHYLUM PROTOZOA—THE SIMPLEST ANIMALS. along with drops of water, which form food vacuoles in thecell substance. Into these vacuoles digestive ferments the digestible parts of the food ha^ been absorbed,the undigested residue is got rid of at any point of theprotoplasm. One or more contractile vacuoles are visiblein the cell substance. T
Outlines of zoology . the cell lies the usually single nucleus. The food consistsof minute Algse, such as diatoms, or of vegetable is reason also to suspect cannibalism. The foodis surrounded by the finger-like processes, and engulfed 90 PHYLUM PROTOZOA—THE SIMPLEST ANIMALS. along with drops of water, which form food vacuoles in thecell substance. Into these vacuoles digestive ferments the digestible parts of the food ha^ been absorbed,the undigested residue is got rid of at any point of theprotoplasm. One or more contractile vacuoles are visiblein the cell substance. They have an excretory function,and serve to get rid of the finer waste products. Life history.—In favourable nutritive conditions theAmoeba grows. At the limit of growth it reproduces bydividing into two. In disadvantageous conditions, such asdrought, it may become globular, and, secreting a cell wallor cyst, lie dormant for a time. The cyst wall is said to bechitinoid. With the return of favourable conditions the. Fig. 35.—Life history of Amceia. I. Amceba with pseudopodia; «., nucleus; ^ contractile vacuole. •^. Divisionin two. 3. Encystation. 4. Escape of Amosba from its cyst. Amoeba revives, and, bursting from the cyst with renewedenergy, recommences the cell-cycle. The conjugation oftwo Amoebae has been observed, and spore - formationoccasionally occurs. Second Type of Protozoa—Actinophrys The Sun-animalcule, Actinophrys sol, is a type of • theHeliozoa. Description. — Like most other Heliozoa, Actinophryslives in fresh water, floating about or rolling over thebottom. It is spherical and minute, measuring at most0-05 mm. in diameter. Long stiff pseudopodia radiateout from the body. A clear axial filament runs up eachpseudopodium, and the small organisms on which Actino- ACTINOPHRVS. 91 phrys feeds are paralysed when they come in contact withthe pseudopodia. The body consists of ectoplasm and endoplasm. Theectoplasm is a thick external layer closely packed
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Keywords: ., bookcentury1900, bookdecade1910, bookidcu3192, booksubjectzoology
