DIFFERENTIAL SUSCEPTIBILITY AS A BASIS FOR 



MODIFICATION AND CONTROL OF EARLY 



DEVELOPMENT IN THE FROG. 



A. W. BELLAMY. 



CONTENTS. 



I. Introduction and General Statement of the Problem 312 



II. Materials and Methods 314 



1. The Susceptibility Method ... 314 



2. Routine and Methods 317 



III. The Origin of Polarity in the Egg. . 318 



1. Polarity in Other Organisms 318 



2. Origin of Polarity in the Frog's Egg 319 



IV. Experimental Data 322 



1. Susceptibility to Lethal Concentrations of External Agents 322 



(a) Unsegmented Eggs 323 



(b) Cleavage Stages 324 



(c) Gastrula Stages 325 



(d) Later Embryonic Stages 326 



2. Experimental Modification and Control of Development 328 



A. Disturbances in Cleavage Such That the Egg Never Gastru- 



lates 332 



(a) Cell Size Ratios . 332 



(b) Bilaterality 333 



(c) The Segmentation Cavity .... 333 



(d) Meroblastic Cleavage 335 



B. Disturbances in Gastrulation 335 



(a) Retardation of the Dorsal Lip Region 336 



(b) and (c) Retardation of Both Dorsal and Lateral Lip 



Regions and Equatorial Gastrulation 337 



(d) Secondary Invaginations 341 



(e) The Gastrular Angle 343 



C. Differential Inhibition in Later Development 344 



V. Discussion . . 346 



i. The Nature of Physiological Axes 346 



2.' Origin of the Dorsal Lip Region 349 



3. The Question of "Specificity" in Vertebrate Teratogeny 351 



VI. Summary. . . 356 



VII. Literature 358 



I. INTRODUCTION AND GENERAL STATEMENT OF THE PROBLEM. 



Observations on vertebrate teratology date almost from the 



beginning of descriptive biology, though active accumulation of 



experimental data on the frog especially, began little more than 



