BLASTOGENIC VARIATIONS. 



107 



sperm, (2) those from stale ova and stale sperm, (3) 

 from stale ova and fresh sperm obtained from another 

 freshly opened Echinoid, (4) from fresh ova and stale 

 sperm, (5) and lastly, from the ova and sperm of the 

 freshly opened Echinoids. It was, of course, impos- 

 sible to get an exact basis of comparison for the larvae 

 obtained from one stale and one fresh sexual product. 

 The best possible was to take a mean between the size 

 of the original normal larvae, and that of the larvae ob- 

 tained from the fresh sexual products used f o* fertilis- 

 ing the stale products. The larvae obtained with both 

 sexual products stale are, of course, accurately com- 

 parable with the original normal larvae. In the ac- 

 companying table an example is given of the mean per- 

 centage differences in the size of the larvae obtained 

 with fresh and stale products, from the original nor- 

 mal larvae in the one case, and from the mean between 

 the original and fresh normal larvae in the other two 



cases. In this experiment, which was the most com- 

 plete made, the fertilisations were performed after 

 keeping the sexual products for respectively 9, 24, 33, 

 and 45 hours. It will be seen that the larvae obtained 

 when both sexual cells were stale were of practically 



