Fig. 5. lacZ-infected chondrocytes were injected into the wing bud of stage 22 chick embryos and incubated for stage 36 (10 days). ß-galactosidase-positive cells were present 24 hours after injection in the humerus (A,B, arrow), i.e. in the proximal region corresponding to the site of injection. After 10 days' incubation, ß-galactosidase activity was present in several tissues, including perimysium (C), tendon (D), bone (E, arrow) and articular fibrocartilage (F, arrow). Using anti-lacZ and bovine-specific collagen type I antibody, bovine cells and collagen were co-localised in articular fibrocartilage (G, arrow), tendon (H, arrow), perimysium (I, arrow) and bone (J, arrow). Samples from animals injected with deep zone cells contained few lacZ-positive cells and when present were not identifiable in any organised tissue (K, arrow).