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New Ideas on the Origin of Bilateral Animals

机译：双边动物起源的新思路

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Comparative anatomy and embryology provide impressive evidence that the ventral side of all Bila-teria (except Chordala) originates from the blastoporal surface, while the mouth and anus develop, respectively, from the anterior and posterior extremities of an elongated blastopore. From the point of view of paleontology, some Vendian multicellular animals represent transitional forms between Radiata and Bilateria. Vendian Bila-teria are metameric organisms with a symmetrical or asymmetrical arrangement of segments; they can be considered as bilaterally symmetrical coelenterates crawling on the oral surface. In the recent Cnidaria, homo-logues of the genes "Brachyury," "goosecoid" and "fork head" are expressed around the mouth. In the recent Bilateria these genes are expressed along the elongated blastopore and around the mouth and anus. These data corroborate the validity of the idea of amphistomy and the homology between the ventral surface in Bilateria and oral disk in coelenterates. It is supposed that the ancestors of Bilateria were crawling on the oral surface (=ventral side) and gave rise to both Fanerozoic Cnidaria and triploblastic Bilateria. This allows us to suggest the origin of Bilateria from Vendian bilaterally symmetrical coelenterates with numerous metameric pockets of the gastral cavity. Such ancestors gave rise to both Cnidaria and Bilateria. Apparently the primary Bilateria were complicated organisms having a coelom and segmentation, which allows us to explain the great diversity of highly organized organisms (arthropods, mollusks, and others) in the Cambrian era. An idea is proposed that Ctenophora are the only group of recent Eumetazoa that retain primary axial symmetry.
机译：比较的解剖学和胚胎学提供了令人印象深刻的证据，表明所有比拉特尔氏菌的腹侧（Chordala除外）都起源于胚盘表面，而嘴和肛门分别从细长的胚盘的前肢和后肢发育。从古生物学的角度来看，一些Vendian多细胞动物代表Radiata和Bilateria之间的过渡形式。 Vendian Bila-teria是具有对称或不对称节段排列的异聚生物。它们可以被认为是在口腔表面爬行的左右对称腔腔。在最近的猪唇草中，“ Brachyury”，“ goosecoid”和“叉头”基因的同源基因在口中表达。在最近的Bilateria中，这些基因沿着细长的芽孢孔以及在嘴和肛门周围表达。这些数据证实了截肢法的有效性以及Bilateria腹侧表面与腔肠动物口腔盘之间的同源性。据推测，Bilateria的祖先在口腔表面（=腹侧）爬行，并引起了Fanerozoic Cndaria和三叶虫性Bilateria的出现。这使我们可以从双侧对称腔腹的Vendian双侧腔腹腔提出Bilateria的起源。这样的祖先同时引起了猪唇草和Bilateria。显然，主要的Bilateria是复杂的生物体，具有体腔和分段功能，这使我们能够解释寒武纪时期高度组织化的生物体（节肢动物，软体动物等）的多样性。提出了一种想法，即C蝶是最近的大头杜鹃中唯一保留主要轴向对称性的一组。

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