1 8 Charles Russell Bardeen 



exposure of the sperm. The external form of some of the larvae 

 preserved is shown on Plates II to V. 



III, May 14. Unsuccessful because ova proved unripe. Be- 

 tween May 5 and May 13, owing to a spell of cool weather, no toads 

 could be obtained. 



IV, May 14. The day was very warm. At the end of the hour 

 and half during which spermatozoa were exposed to the rays both 

 experiment and control spermatozoa were non-motile and proved 

 incapable of fertilizing any ova. 



V, May 15. Sperm exposed an hour and a half. A considerable 

 proportion of the control ova were fertilized. Only a few of the 

 experiment ova were fertilized. Of these only one developed past 

 the early cleavage stages. On May 22, at three o'clock, p. m., this 

 larva, which was small, unsymmetrical and ill-developed, appeared 

 about to die. It was, therefore, killed and preserved. Micro- 

 scopically it presented the features characteristic of the tadpoles 

 developed from ova fertilized by irradiated sperm. 



VI, May 16. Sperm exposed one and a quarter hour. At the 

 end of this period neither irradiated nor control spermatozoa 

 proved capable of motion or of fertilizing. The day was an 

 exceedingly warm one. 



VII, May 16. Sperm exposed one-half hour to the rays. Of 

 the control ova only about 20 per cent were fertilized. These 

 developed normally. Of the experiment ova only three or four 

 per cent were fertilized. None of these developed past the gas- 

 trula stage. 



Structure of the Larvcs 



At the time of or soon after the hatching of the larvas abnormal 

 structural differentiation began to make an externally visible dis- 

 tinction between those experiment larvae which developed best 

 and the control larvae. In the experiment larvae the tails all 

 showed more or less abnormality of form and the larvae with a few 

 exceptions proved incapable of swimming, although some were 

 capable of irregular movements of the body and tail. In length 

 the experiment larvae did not grow much after this period. In 

 width and thickness the growth was greater but was in large part 



