[Comparative and quantitative ultrastructural study of the olfactory organs of four strains of domestic pigeons].

1. By counting the axons per micron 2 on electronmicrographs of cross-sectioned olfactory nerves and multiplying this number by the area of the cross-sectioned nerves, the number of olfactory receptors was determined in 4 breeds of domestic pigeons including homing pigeons. 2. The total number of olfactory receptors varied between 3.0 and 7.4 . 10(6). It significantly depended on the body size of the pigeons. There was no evidence for differences in the number of olfactory receptors between the breeds independent of body size. 3. No differences in the relative size of the olfactory bulbs could be detected between the breeds. 4. The ultrastructure of the olfactory epithelium was basically similar to that of other birds. The covering mucus layer was revealed to be a secretion product of both the olfactory glands of Bowman and the olfactory supporting cells. No differences were observed in the ultrastructure of the olfactory region between the four breeds investigated.