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| | The Metazoa |
 | | Thus Sagitta is temporarily coelenterate, but the two gastrovascular sacs, each enclosing an entercoele, become shut off from the alimentary canal and metamorphosed into the walls of the perivisceral cavity. |
 | | In the Brachiopoda, there is some ground for thinking that the perivisceral cavity is formed in the same way as in Sagitta and the Echinodermata; while, in the Lamellibranchiata and Odontophora, there is every reason to believe that the perivisceral cavity is formed by splitting of the mesoblast, or that they are schizocoelous. |
 | | In the lowest Tunicata, represented by Appendicularia, the recent investigations of Fol have shown, that, in the adult, the body proper is formed almost exclusively by an ectoderm and endoderm, which proceed directly from the epiblast and hypoblast of the embryo. |
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