A Junior Course of Pracical Zoology

Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. Excerpt from book: Section 3PEACTICAL ZOOLOGY. Chapter I. THE PROTOZOA. A Pkotozoon is an animal which consists of only one cell, the equivalent of a single cell of any of the tissues of a higher animal. Protozoa are always of small size, and are usually microscopic. I. AMCEBA. This protozoon is found at the bottoms of freshwater pools, and in damp situations. Its indefinite and ever-changing shape is characteristic, and has gained for it the name ' proteus animalcule.' There are several forms, the largest of which are just visible to the naked eye, while others are exceedingly minute. textit{Place a drop of water containing Amoeba on a slide: cover; and search for the animals with a low power of the microscope. When found, examine them with a hiijh power. A. General appearance. The animal is an irregular mass of protoplasm, running out into blunt processes or pseudopodia, the protrusion andretraction of which cause great changes in the form of the cell. The pseudopodia may branch slightly. B. Structure. The whole body is a naked mass of protoplasm, which is of two kinds. 1. The ectosarc is the clearer outer portion of the body. d2R--*V Fv j.3. !, -XT Rg.4 Flg:5. ' Ft*6 cA fr Fig. 8. Fios. 1 to 8.?Amoeba; x 400. (o. H. H.) Figs. textit{2 and 3 were drawn from the same specimen, which was moving in the direction shown by the arrow. Fig. 4 is a form with branch- ing pscudopodia. Figs. 5 to 8 were drawn from one specimen at intervals of about twenty seconds. N, nucleus. P, pseudopodium. PV, pulsating vacuole. textit{. The endosarc is the granular and usually more fluid central portion. Its flowing movements, which accompany the protrusion and retraction of the pseudopodia, are rendered obvious by the granules contained in it. textit{Withi...