Studies on the Mechanism of Meristic Segmentation: I. The Dimensions of Somites

Abstract

The dorso-ventral thickness of the mesoderm sheet in Urodele embryos was altered by adding or removing material on the ventral side at the beginning of gastrulation. Similar alterations were made at a later stage of development by direct removal or addition of archenteron roof in late gastrulae. Whenever these operations were successful in changing the height of the somites, there was evidence that their anterior-posterior length was altered in the same sense. In spite of considerable variability in the material, the correlation of somite height and length is significant when a large number of observations are considered together. The bearing of this relation between height and length on the biophysical theories of metameric segmentation is briefly discussed.