They say that its folds enclose the blastopore, and that, therefore, when they come together, a neurenteric canal is formed. How does the the blastopore lip form A small group of cells change shape, narrowing at the exterior edge of the blastula. The plesiomorphic condition, found in the Protostomes, is for the blastopore to become the mouth. Scott and Osborn, in their account of the development of the newt, describe a posterior dilatation of the medullary canal, the sinus rhomboidalis, which remains open for some time after the rest of the canal has closed. This blastopore-to-anus developmental pathway is found in Chordata, Hemichordata, Echinodermata (starfish, sea urchins, sea cucumbers, etc.), uniting these groups into a monophyletic group called the Deuterostomes. He suggested to me afterwards that I should attempt to test this observation by cutting sections of the embryos, and my results fully confirm what he previously stated. Sedgwick mentions that he was led to conclude from surface views of a large number of stages that the blastopore of the newt ( Triton cristatus) does not close, but persists as the anus.

In a paper lately published on “The Origin of Metameric Segmentation,” Mr. Future mesodermal and endodermal cells sink down into the interior, leaving only the ectodermal material at the surface.

Fate of blastopore birds