The evolution of man: a popular exposition of the principal points of human ontogeny and phylogene . Fig. 280.—A simple Gliding Worm {Rhahdocoeum) m, mouth; sd, throat-epithelium ; sm, throat muscle-mass ; d, stomach-intestine ; nc, renal ducts ;/, ciliated outer-skin ; nm, openings of the latter ; au, eye ; na, nose-pit. Fig. 281.—Structure of an Ascidian (seen from the left side, as in PlateXI. Fig. 14). The dorsal side is turned toward the right, the ventral side tothe left; the mouth-opening (o) is above ; at the opposite, tail end, theascidian has become adherent. The gill-intestine (br),
The evolution of man: a popular exposition of the principal points of human ontogeny and phylogene . Fig. 280.—A simple Gliding Worm {Rhahdocoeum) m, mouth; sd, throat-epithelium ; sm, throat muscle-mass ; d, stomach-intestine ; nc, renal ducts ;/, ciliated outer-skin ; nm, openings of the latter ; au, eye ; na, nose-pit. Fig. 281.—Structure of an Ascidian (seen from the left side, as in PlateXI. Fig. 14). The dorsal side is turned toward the right, the ventral side tothe left; the mouth-opening (o) is above ; at the opposite, tail end, theascidian has become adherent. The gill-intestine (br), perforated by manyopenings, extends into the stomach-intestine. The terminal intestineopens through the anus (a) into the gill-cavity {cl), from which the excre-ment is passed out with the respirated water through the gill-pore, or cloacalopening (a) ; m, mantle. (After Gegenbaur.) 328 THE EVOLUTION OF become a respiratory organ. I have already pointed outhow characteristic this adaptation is of Vertebrates andMantle Animals {Tunicata, p. 87). Thephylogenetic origin of the gill-openin
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Keywords: ., bookcentury1800, booksubjectembryologyhu, booksubjecthumanbeings
