The evolution of man : a popular exposition of the principal points of human ontogeny and phylogeny . ivnv. Fig. 280.—A simple Gliding Worm (Rhabdoccehim) m, mouth; sd, throat-epithelium ; sm, throat muscle-mass; d, stomach-intestine; nc, renal ducts;/, ciliated outer-skin; », openings of the latter ; em, eye; na, nose-pit. Fig. 281.— Structure of an Ascidian (seen from the left side, as in PlateXL Fig. 14). The dorsal side is turned toward the right, the ventral side tothe left; the mouth-opening (0) 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 phylogeny . ivnv. Fig. 280.—A simple Gliding Worm (Rhabdoccehim) m, mouth; sd, throat-epithelium ; sm, throat muscle-mass; d, stomach-intestine; nc, renal ducts;/, ciliated outer-skin; », openings of the latter ; em, eye; na, nose-pit. Fig. 281.— Structure of an Ascidian (seen from the left side, as in PlateXL Fig. 14). The dorsal side is turned toward the right, the ventral side tothe left; the mouth-opening (0) 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 (a1) ; m, mantle. (After Gegenbaur.) 328 THE EVOLUTION OF MAN. t nv- d im become a respiratory organ. I have already pointed outhow characteristic this adaptation is of Vertebrates and Mantle Animals (Tunicata, p. 87). Thephylogenetic origin of the gill
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