the Echinoderm Egg during Fertilisation. 



223 



the fusion of the pronuclei is taking place. At the 40th to 45th minute 

 it begins to rise again and this synchronises with the first segmentation 



20 40 MINUTES. 60 



Fig. 3. — Graph showing the oxygen consumption and carbon dioxide output of a quantity 

 of E. microtuberculatus eggs that contained 2"8 mgrm. of egg nitrogen during the 

 course of the first hour following fertilisation. It will be seen that the steepest 

 part of the curve is in the first 15 minutes, while the sperm are in relation with the 

 egg membrane. At the 25th minute, when the male and female pronuclei are 

 undergoing fusion, there is a slight flattening of the curve. 



division. The steepest part of the curve is that in the first 10 minutes 

 interval, which corresponds to the action of the sperm on the external surface 

 of the egg membrane. 



