FURTHER STUDIES ON THE VARIATION IN SUS- 

 CEPTIBILITY OF AMPHIBIAN OVA TO THE X-RAYS 

 AT DIFFERENT STAGES OF DEVELOPMENT 



CHARLES RUSSELL BARDEEN 

 Fro7n the Anatomical Laboratory, University of Wisconsin 



EIGHTEEN FIGURES 



CONTENTS 



Introduction 420 



1 Effects of exposure of spermatozoa to the x-rays 435 



1 Fertilization 436 



2 Period of cleavage 437 



3 Gastrulation 438 



4 Period of larval differentiation 439 



General effects 440 



External form 441 



Internal structure 441 



5 Tadpole stage 445 



Conclusions 446 



2 Effects of the exposure of mature ova to the x-ray 450 



1 Fertilization 451 



2 Period of cleavage 452 



3 Period of gastrulation 452 



4 Period of larval differentiation 453 



5 Tadpole period 454 



Comparison of the results of exposure of spermatozoa and of 



mature ova 454 



3 Action of the x-rays on fertilized ova and on larvae : 457 



Introduction 457 



1 Period of fertilization 458 



2 Period of relative immunity 462 



3 Early cleavage stages 464 



Effects of temperature 472 



4 Advanced cleavage and gastrulation stages up to the closure of 



the blastopore (12 to 36 hours after fertilization) 474 



5 Period from the closure of the blastopore to the period of hatching 481 



6 From the period of hatching to the period of metamorphosis 482 



7 Period of metamorphosis 485 



4 Summary of experiments 486 



Bibliography 492 



419 



THE AMERICAN JOURNAL OF ANATOMY, VOL. 11, NO. 4. 



