Increase in volume of the chick wing bud at the beginning of its development

Serial sections in the transverse body plane were used to determine the volume of the limb bud and of its parts--namely, the apical ectodermal ridge, the ectodermal epithelium, the coat zone, the vascular zone, and the plug during the period between the onset of its formation (Hamburger and Hamilton's stage 17) and the stage of nerve fibre ingrowth (HH 22 +). During that period the anlage of the wing was shown to increase in volume, mainly by increasing in length, with the increase being more than 8 times during a 28 hr incubation. Various components differed in their growth rate. The apical ectodermal ridge did not increase at all. The part that increased most--48 times--was the plug which gives rise to the cartilaginous primordium of the skeleton of the wing. The proportions of the various zones changed markedly during growth.