Fig. 2. Histochemical staining for ßgal⁺ in wholemounts of W^lacZ/+ mice. (A) At E9.5, ßgal⁺ cells (arrows) are present in the cervical region of the embryo on the dorsal midline; no ßgal⁺ cells were observed elsewhere in the ectoderm. (B) Low-power view of an E10.5 embryo showing strong ßgal⁺ cells along the dorsal midline (arrows), and lateral to it under the ectoderm. (C) High-power view of the boxed area in B, showing ßgal⁺ cells on the dorsal midline and emanating from it (arrows). (D) Montage of images from the trunk of an E11 embryo, showing ßgal⁺ cells distributed extensively under the ectoderm. dm, dorsal midline. Scale bars: 0.5 mm.