. Comparative anatomy. Anatomy, Comparative. NOTOCHORO' MOUTH' I ^"*''^''* IPHARYCEAL POOCH CEPHALODISCUS. Fig. 536.—A diagram of Cephalodiscus viewed from the left side as if in median optical section. The presence of a notochord in the pre-oral lobe is one of the reasons for placing this animal among hemichordates. While not regarded as a form "ancestral" to vertebrates, cephalodiscus interests morphologists as a primitive chordate. (Redrawn after W. Patten.) As a result, Brooks totally rejected the dogma that vertebrates are modified annelids and the assumption that tunicates
. Comparative anatomy. Anatomy, Comparative. NOTOCHORO' MOUTH' I ^"*''^''* IPHARYCEAL POOCH CEPHALODISCUS. Fig. 536.—A diagram of Cephalodiscus viewed from the left side as if in median optical section. The presence of a notochord in the pre-oral lobe is one of the reasons for placing this animal among hemichordates. While not regarded as a form "ancestral" to vertebrates, cephalodiscus interests morphologists as a primitive chordate. (Redrawn after W. Patten.) As a result, Brooks totally rejected the dogma that vertebrates are modified annelids and the assumption that tunicates are degenerate vertebrates. He regards the free-swimming appendicularia as the type from which chordates have evolved, and thus revives the tunicate theory of vertebrate ancestry. The many points of resemblance of appendicularia STATIC ORGANV. >ENDODERM STRAND PHARYNX- GILL SLITS'" OCELLUS) (HE^T Fig. 537.—Diagram of a larval urochordate. The similarity of the larval uro- chordate to the embryo of a cephalochordate (amphioxus) suggests that a form like this lies near the main line of vertebrate ancestry. (Redrawn after von Beneden and Julin modified.) to amphioxus, and the similarity of their development, give a strong foundation to this hypothesis. Appendicularia, like the larvae of other tunicates, is obviously a chordate with fundamental chordate traits— notochord, hollow dorsal nerve cord, expanded "brain" vesicle, gill- slits, endostyle, and ventral heart. Indeed, the resemblances between tunicates and amphioxus led Minot to suggest that the urochordates and cephalochordates should be grouped together as 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. Blakist
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