420 GRACE MEDES 



Fisher ('03), also working on Arbacia at Woods Hole, per- 

 formed somewhat similar experiments using diluted sperm-sus- 

 pensions at various intervals to fertilize freshly extruded eggs. 

 In some instances the last successful fertilization he was able 

 to obtain was 24 hours after the sperm was removed from 

 the male. In one case, the sperm was still able to fertilize the 

 eggs after 133 hours, 30 minutes, and Fisher thought possibly 

 it might have been active longer had he been able to continue 

 the experiment. He found that "whenever fertilization occurs 

 the fertilized egg develops to the adult stage .... never 

 was a segmented egg found that did not develop into a pluteus." 

 In this respect, his results disagree with those obtained above, 

 where a slight effect on the size and a still greater effect upon 

 the vigor of the resulting individuals were obtained. 



Goldfarb ('15), made a similar study with Toxopneustes 

 variegatus, and in most respects the results of this investigation 

 agree with his. He found that 'increasingly stale eggs of a 

 given female, though fertilized by freshly prepared sperm sus- 

 pensions, at each trial gave a decreasing number of fertiliza- 

 tions, and that this decrease was approximately the same for all 

 females The rate of cleavage is progressively re- 

 tarded. The number that cleave irregularly is increased The 

 number of atypic larvae is correspondingly increased." But his 

 results disagree with those in this study, in the experiment ? 

 with fresh eggs X stale sperm and stale eggs X fresh sperm. In 

 both cases development was normal. Possibly the germinal 

 products employed by Goldfarb had not been kept so long as 

 those in the experiment above, or else Toxopneustes sperm and 

 eggs may differ in /lability from those of Arbacia. 



DISCUSSION 



We have seen that the control cultures in the previous ex- 

 periments exhibited wide variation. As the plot containing the 

 curves of the general averages shows, the condition of the larvae 

 24 hours old varies from no skeleton to one of 44.83, which is 

 slightly larger than that of the control of Experiment 18 (sea- 

 water + NaCl), 72 hours old. The widest variation is found in 



