First lesson in zoology : adapted for use in schools . tion, but rather the cause of it. While we do not, and may never, know what life is, wecan yet understand that the protoplasm which forms thebodies of the simplest beings is only the vehicle or mate-rial in and through which the life-forces act. The ulti-mate origin of what we call life is thus far an inscrutablemystery. LiTERATXJEB. Kent. Manual of the Infusoria. London, Microscopy for Beginners. Philadelphia, et Lachmann. fitudes sur les Infusoires et les Rhizo-podes. Genfeve, Der Organismus
First lesson in zoology : adapted for use in schools . tion, but rather the cause of it. While we do not, and may never, know what life is, wecan yet understand that the protoplasm which forms thebodies of the simplest beings is only the vehicle or mate-rial in and through which the life-forces act. The ulti-mate origin of what we call life is thus far an inscrutablemystery. LiTERATXJEB. Kent. Manual of the Infusoria. London, Microscopy for Beginners. Philadelphia, et Lachmann. fitudes sur les Infusoires et les Rhizo-podes. Genfeve, Der Organismus der Infusionsthiere, 1-3. Protozoa, in Bronns Klassen und Ordnungen, etc. 1891. CHAPTEE SPONGES. It 18 a great step from an inJusorian to a sponge—^from aone-celled to a many-celled animal. Formerly sponges weresupposed to be plants, but they are now known to be com-posed of numerous cells, arranged in three layers, and todevelop from eggs like the higher animals. A sponge, then, is a cellular sac (Fig. 16) with digestive. FlQ. 16.—A longitudinal section through a simple calcareous sponge, showing thesimple central cavity; 6, showing a single osculum at the top, and the manymouths over the surface. chambers or minute rude stomachs lined with ciliated cells,the whole sponge-mass being supported by an irregularbasket-work of needle-like bodies called spicules (Fig. 17). 22 FIRST LB880NS IN ZOOLO&T. Upon cutting a dry sponge in half there are to be seen largecanals which have large openings called oscula; these arereally openings for the exit of waste matters. Among theselarge openings are multitudes of minute openings whichserve as mouths. These mouths lead by branching canals
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1894
