. The causes and course of organic evolution; . — soc —mc s9ac. Fig. 23.—Diagram of Rotifer to left, of gasteropodous embryo to right,, apical area; , )., basal area; m, mouth; a., an., anus; , ,dorsal brain; , , ventral ganglia; e, eyes; nep., , nephridia; I, liver; t,tentacles; s, shell; , shell gland. Compare also with Fig. 25 a., p. 534. some ancient rotifers formed a dorsal, later also a ventral,and still later two lateral plates that fused as the tubular loricaof various genera. Of these four, the dorsal and ventral havebeen retained and expanded in Bra
. The causes and course of organic evolution; . — soc —mc s9ac. Fig. 23.—Diagram of Rotifer to left, of gasteropodous embryo to right,, apical area; , )., basal area; m, mouth; a., an., anus; , ,dorsal brain; , , ventral ganglia; e, eyes; nep., , nephridia; I, liver; t,tentacles; s, shell; , shell gland. Compare also with Fig. 25 a., p. 534. some ancient rotifers formed a dorsal, later also a ventral,and still later two lateral plates that fused as the tubular loricaof various genera. Of these four, the dorsal and ventral havebeen retained and expanded in Brachiopoda, the dorsal maybe the cuticular shell, and the two laterals the future calcifiedshells of Lamellibranchiata, while the dorsal shell alone haspersisted in Gasteropoda. Such theoretical points suggestthe need for a careful reexamination of lorica formation inrotifers, and particularly a more detailed study of the characterand cytological nature of the cells that secrete the lorica. As the free-swimming veliger matures and then passes intothe creeping
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