Formation of the Coelom
Formation of the Coelom
The coelom, or true body cavity that contains the viscera, may be formed by one of two methods (see Figure 8-9)— schizocoely (Gr. schizein, to split, + koilos, hollow or cavity) or enterocoely (Gr. enteron, gut—or by modification of these methods. In schizocoelous formation, the coelom arises, as the word implies, from the splitting of mesodermal bands that originate from the blastopore region and grow between the ectoderm and endoderm; in enterocoelous formation, the coelom comes from pouches of the archenteron, or primitive gut.
These two quite different origins for the coelom are another expression of the deuterostome-protostome dichotomy of bilateral animals. The coelom of protostomes develops by the schizocoelous method. Deuterostomes primitively follow the enterocoelous plan. Vertebrates, however, are exceptions to this distinction because their coelom is formed by mesodermal splitting (schizocoelous). This is a derived condition that evolved in early vertebrates to accommodate large stores of yolk during development.
The coelom, or true body cavity that contains the viscera, may be formed by one of two methods (see Figure 8-9)— schizocoely (Gr. schizein, to split, + koilos, hollow or cavity) or enterocoely (Gr. enteron, gut—or by modification of these methods. In schizocoelous formation, the coelom arises, as the word implies, from the splitting of mesodermal bands that originate from the blastopore region and grow between the ectoderm and endoderm; in enterocoelous formation, the coelom comes from pouches of the archenteron, or primitive gut.
These two quite different origins for the coelom are another expression of the deuterostome-protostome dichotomy of bilateral animals. The coelom of protostomes develops by the schizocoelous method. Deuterostomes primitively follow the enterocoelous plan. Vertebrates, however, are exceptions to this distinction because their coelom is formed by mesodermal splitting (schizocoelous). This is a derived condition that evolved in early vertebrates to accommodate large stores of yolk during development.
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