. Chordate anatomy. Chordata; Anatomy, Comparative. E ECHINOOERM, F HEMICHORDATE. G UROCHORDATE, H. CEPHALOCHORDATE. Fig. 375.— Diagrams of embryonic stages illustrating the contrast in the fate of the blastopore in various groups of animals. The forms in which the embryonic blastopore becomes the mouth were grouped together by Grobben as PROTEROSTOMIA. The DEUTEROSTOMIA include those animals in which the blastopore becomes the anus or lies in the anal region. The coelenterates, flatworms, annelids, and molluscs are Proterostomians, while echinoderms and chordates are Deuterostomians. A somewh
. Chordate anatomy. Chordata; Anatomy, Comparative. E ECHINOOERM, F HEMICHORDATE. G UROCHORDATE, H. CEPHALOCHORDATE. Fig. 375.— Diagrams of embryonic stages illustrating the contrast in the fate of the blastopore in various groups of animals. The forms in which the embryonic blastopore becomes the mouth were grouped together by Grobben as PROTEROSTOMIA. The DEUTEROSTOMIA include those animals in which the blastopore becomes the anus or lies in the anal region. The coelenterates, flatworms, annelids, and molluscs are Proterostomians, while echinoderms and chordates are Deuterostomians. A somewhat similar view is that of Grobben who divides animals into two phylogenetic series based upon differences in the fate of the primitive mouth or blastopore. The forms in which the blastopore becomes the adult mouth (or cardiopore) reach their evolutionary climax in arthropods and molluscs. Those, on the other hand, in which the blastopore becomes APICAL PLATE CARDIOPORE STOMODEXWi. PBEORAL CIUATID ntOTOCPHRIDIUM * MUOOERM Fig. 376.—A diagram of a trochophore larva According to Delsman's theory of the origin of vertebrates, the cardiopore (blastopore) of the trochophore larva is homologous with the neurenteric canal of vertebrates. In other words, the relatively short stomo- deum of the annelid is stretched to become the neural tvibe of vertebrates. (Redrawn after Hatschek.) the anus or lies near the anus lead to the chordates and vertebrates. (I^'ig- 375) A third attempt to solve the phylogenetic problem on the basis of embryological evidence is that of Delsman, who derives chordates, annelids and molluscs from a form like that of the trochophore larva characteristic. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Neal, Herbert V. (Herbert Vincent), 1869-1940; Rand, Herbert W. (Herbert Wilbur), 1872-196
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