Effects of complete tail bud extirpation on early development of the posterior region of the chick embryo

The tail bud was completely extirpated down to the yolk from 65 embryos at stages 13‐17 to determine whether the posterior part of the noto‐chord originates from the tail bud or from a more anterior region (i.e., prospective notochordal region). About 40% of the 44 surviving embryos developed near‐normal tails, con̈taining a localized defective region beginning near the base of the tail and extending a short distance posteriorly, about 15% developed truncated, cone‐shaped tails, containing a defective region beginning near the base of the tail and extending towards the tip, and about 45% developed short, ventral tail remnants, containing a localized defective region beginning near the base of the tail and extending a short distance posteriorly. The tail was absent in only one embryo. These differences were probably due primarily to variation in the amount of healing and regeneration that occurred, and were independent of the stage at which the operation took place. The tail region has a tremendous capacity for regeneration since a near‐normal tail frequently developed. The location of the beginning of the defective region near the base of the tail suggests that the tail bud primarily gives rise to tail structures. All embryos had neural tube defects, about 30% developed large, midline somites within the defective region, and about 25% developed an ourenteric outgrowth. The notochord was always normal within the defective region. These results are consistent with the view that the tail bud contributes cells to the posterior part of the neural tube, but not to the notochord.