Models of Development: Experimental Embryology of Echinoderms . Sven Horstadius. Clarendon (Oxford University Press), New York, 1973. x, 192 pp., illus. $16.; Developmental Biology of the Sea Urchin Embryo . Giovanni Giudice. Academic Press, New York, 1973. x, 470 pp., illus. $32.; Sea Urchin Development . Cellular and Molecular Aspects. Louis W. Stearns. Dowden, Hutchinson and Ross, Stroudsberg, Pa., 1974. xii, 340 pp., illus. $20.