Fig. 6. Angular rotation of 1-day-old (neural tube stage) embryos of red-eyed treefrogs in the 5 min after moving them to different initial positions within the egg. Grey background indicates egg surface covered by other eggs and leaf substrate; white background represents air exposure and zone of higher perivitelline oxygen levels. Experimental embryos positioned with their developing head at the hypoxic rear of the egg moved it toward the air-exposed surface (A,B), whereas controls positioned with their developing head at the front of the egg remained there (C,D). Data are means ± s.e.m.; N=25 embryos per treatment.