. Comparative anatomy. Anatomy, Comparative. NOTOCHORD ENDOSTYLE CLUB-SHAPED GLAND. ENTERON C. AMPHIOXUS EMBRYO. ANTERIOR . CAVITY ENDOSTYLE' CLUB-SHAPED GLAND 1ST (TRANSIENT)GILL-SLIT D. AMPHIOXUS OLDER EMBRYO. Fig. 278.—While gill-slits occur both in urochordates and in cephalochordates (Amphioxus), evidence is lacking that the anteriormost gill-slits of the two groups can behomologized. Those of the urochordate are permanent, while those of amphioxus do not persist as functional gills. The first pair of pouches in amphioxus become the endostyle, the second pair form the transient larval clu
. Comparative anatomy. Anatomy, Comparative. NOTOCHORD ENDOSTYLE CLUB-SHAPED GLAND. ENTERON C. AMPHIOXUS EMBRYO. ANTERIOR . CAVITY ENDOSTYLE' CLUB-SHAPED GLAND 1ST (TRANSIENT)GILL-SLIT D. AMPHIOXUS OLDER EMBRYO. Fig. 278.—While gill-slits occur both in urochordates and in cephalochordates (Amphioxus), evidence is lacking that the anteriormost gill-slits of the two groups can behomologized. Those of the urochordate are permanent, while those of amphioxus do not persist as functional gills. The first pair of pouches in amphioxus become the endostyle, the second pair form the transient larval club-shaped gland, the left third gill pouch disappears early in ontogenesis. As shown in D the anterior endodermic diver- ticula (anterior cavities) resemble gill pouches in relations and in mode of origin. the intestinal diverticula of flatworms. Were these diverticula to meet the skin and become perforate, apertures similar to gill sUts would be formed. Gill slits first appear in the hemichordates. Rhabdopleura has none, but cephalodiscus has a single pair. In most hemichordates the number is considerable and increases throughout Hfe. Early in their development, their number is doubled by the growth of "tongue-bars" which extend from the dorsal side of the gill aperture to the ventral side. Later 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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