478 CHARLES RUSSELL BARDEEN 



per cent. None of these tadpoles lived more than two weeks 

 after exposure. In experiment B-33|, however, exposure thirty- 

 three and one-half to thirty-four and one-quarter hours after 

 fertilization, all the eggs developed into normal tadpoles and a 

 considerable number of these were followed through metamorpho- 

 sis. At the time of exposure this group of eggs had moderate 

 sized or very small blastopores. 



The results summarized in table 6, Experiments C and D fol- 

 lowed the exposure of successive groups from two batches of eggs 

 in which the control specimens showed a considerable percentage 

 of defective and abnormal larvae, (about 18 per cent in each case.) 

 The causes of the defects are uncertain. The eggs in each case 

 were laid while the female was in captivity and were fertilized by 

 a male present in the same jar. There was a small amount of 

 water in the jar and possibly the eggs were in some way poisoned. 

 It was late in the season so that there is also a possibility that the 

 eggs were over-ripe. The exposure of each of the groups of eggs 

 was for thirty minutes. The exposed eggs showed a greater per- 

 centage of larvae which failed to develop into free swimming tad- 

 poles than the control. In both groups the eggs from the thir- 

 teenth to the fifteenth hour, before gastrulation was apparent, 

 showed less susceptibility than in the seventeen and nineteen 

 hours when the process of gastrulation was commencing. A simi- 

 lar decreased susceptibility preceding gastrulation was not clearly 

 marked in the groups previously described. In Experiments C and 

 D the development of the tadpoles was not followed more than two 

 weeks after fertilization so that the number capable of ultimate 

 normal development was undetermined. 



The internal changes found in abnormal larvae and tadpoles 

 derived from eggs exposed during the period of gastrulation seem 

 essentially similar to those found in larvae derived from exposed 

 sex cells. In general, however, the alterations produced seem to 

 be somewhat more diffused in the former than in the latter. 

 After exposure of the spermatozoa and to a less extent after 

 exposure of the ova before fertilization one not frequently finds 

 the abnormalities confined mainly to a restricted part of the body 

 or to a single organ system, but when specimens are exposed dur- 



