The doctrine of descent and The doctrine of descent and Darwinism doctrineofdescen00schm Year: 1896 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 diam-am rives 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. c. sists of two strata, or layers of cells. The cells of the external stratum are distinguished from those of the i
The doctrine of descent and The doctrine of descent and Darwinism doctrineofdescen00schm Year: 1896 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 diam-am rives 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. c. 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- 5
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