. Comparative anatomy. Anatomy, Comparative. PROTONEPHRIOIUM- MESODERM Fig. 522.—A diagram of a trochophore larva. According to Delsman's theory of the origin of vertebrates, the cardiopore (blastopore) of the trochophore larva is homolo- gous with the neurenteric canal of vertebrates. In other words the relatively short stomodeum of the annelid is stretched to become the neural tube of vertebrates. (Redrawn after Hatschek.) he claims, processes which occur in early development serve to explain why the neural tube does not elongate in this fashion. The backward growth of the blastopore in vert
. Comparative anatomy. Anatomy, Comparative. PROTONEPHRIOIUM- MESODERM Fig. 522.—A diagram of a trochophore larva. According to Delsman's theory of the origin of vertebrates, the cardiopore (blastopore) of the trochophore larva is homolo- gous with the neurenteric canal of vertebrates. In other words the relatively short stomodeum of the annelid is stretched to become the neural tube of vertebrates. (Redrawn after Hatschek.) he claims, processes which occur in early development serve to explain why the neural tube does not elongate in this fashion. The backward growth of the blastopore in vertebrate embryos involves the extension CHORDATE TROCHOPHORE ANNELID NEUROPORE( BLASTOPORE, NEURAL TUBE\ ENTERON FOREGUT MOUTH VnuS ! ''BLASTOPORE EYE. ^^-ANUS MOLLUSC Fig. 523.—Diagram illustrating the theory of Delsman that by change in the loca- tion of the growth center a trochophore (A) may be converted into either a chordate (B), or a mollusc (C), or an annelid (L>). of the neural plate caudad. According to Delsman this is not a process of concrescence, as is sometimes assumed, but a true process of backward growth. This precocious backward growth takes the place of the back- ward elongation of the neural tube. The result is the same as if there had been an elongation of the neural tube—the blastopore is carried to the posterior end of the body, where it persists for a while as the. 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), 1872-1960. Philadelphia : P. Blakiston's Son
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