Limb Development in the Absence of Ectodermal Ridge

Abstract

THIS communication is designed to indicate the current status of research concerned with the importance of ectoderm in limb morphogenesis in the chick embryo. Previous studies^1,2,3 indicate that the apical ectodermal ridge serves as an inductor of limb outgrowth, and that elaboration of distal structures ceases when it is removed. The experiments which provide the evidence for the importance of the apical ectodermal ridge are based on surgical procedures¹ and on techniques which involve the use of a chelating compound for preparing ectoderm-free mesoderm and trypsin for preparing mesoderm-free ectoderm². Recently Bell⁴ has postulated that the ectoderm may not be necessary for limb elaboration, a view which has also been taken by Amprino and Camosso⁵. In Bell's experiments, 19 per cent of limb bud stripped of ectoderm by means of focused ultrasound and grafted to the flank or cœlom formed skeletal parts representative of all proximo-distal levels of the limb.