The embryogenesis of the subclavian glomera (aortic bodies) is controversial. Past investigators have attributed the development of the Type I cells to mesodermal and/or neural elements. Based on the results of the present light microscopic, fluorescence histochemical and electron microscopic study of rabbit aortic bodies from 16 days of gestation (term:31 days) to four days postpartum, it appears that the Type I glomus cell are derived from cells of neural crest origin. The subclavian anlage is associated with cells of neural crest origin. The subclavian glomus anlage is associated with cells of vagal origin throughout its development. Evidence of Type I cell development from pre-existing mesodermal condensations is not observed. Type I cells exhibit formaldehyde-induced-fluorescence by the twentieth day of gestation. Dense-cored cytoplasmic vesicles are apparent by the sixteenth day of gestation. The number of cytoplasmic vesicles increases steadily, but the greatest increase of vesicles is observed between the twenty-eighth day of gestation and birth. Primitive Type I glomus cells exhibit abundant polysomes and rough endoplasmic reticulum indicative of synthetic activity. Nerve terminals are apparent adjacent to Type I cells by the twentieth day of gestation, but synaptogenesis does not occur until sometime between the twenty-fourth and twenty-eighth days of gestation. Abundant vascularity, characteristic of chemosensory glomera, is not achieved until the twenty-eighth day of gestation.