Fig. 1.—Culture dish with four microdroplets of media under light-weight paraffin oil. Approxinately original size.

Fig. 2.—Two-cell mouse ova at beginning of in vitro culture. ×60.

Fig. 3.—Eight-cell stage. Developed from two-cell mouse ova cultured in vitro for 24 hr. ×60.

Fig. 4.—Morulae and early blastocysts. Developed from two-cell ova cultured in vitro for 48 hr. ×60.

Fig. 5.—Late blastocyst escaping from zona pellucida. Developed from two-cell ova cultured in vitro for 72 hr. ×60.

Fig. 6.—Late blastocyst completely free of zona. Developed from two-cell ova cultured in vitro for 72 hr. ×120.