. The doctrine of descent and Darwinism. Evolution. EARLIEST CONDITION OF LARVA. 51 to the later and actual typical impress. With this object, let us consider the larva of a calcareous sponge at. the stage which Haeckel has designated as the Gastrula phase. The diagram gives the section of a larva of this description, which at this period is nothing more than a stomach provided with an orifice (fig. 5 <?) ; its wall con-. FIG. 5- sists of two strata, or layers of cells. The cells of the external stratum are distinguished from those of the inner one by their elongated form, and the possessio
. The doctrine of descent and Darwinism. Evolution. EARLIEST CONDITION OF LARVA. 51 to the later and actual typical impress. With this object, let us consider the larva of a calcareous sponge at. the stage which Haeckel has designated as the Gastrula phase. The diagram gives the section of a larva of this description, which at this period is nothing more than a stomach provided with an orifice (fig. 5 <?) ; its wall con-. FIG. 5- sists of two strata, or layers of cells. The cells of the external stratum are distinguished from those of the inner one by their elongated form, and the possession of filaments serving as organs of locomotion. All subse- quent development and differentiation, certainly not very important in the sponges, may be traced to modi- fications of these two membranes ; the external mem- E 2. 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 Schmidt, Dr. (Eduard Oskar), 1823-1886. London, H. S. King & Co.
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