the Echinoderm Egg during Fertilisation. 



219 



being arrived at by deducting the readings of the CO2 manometer from the 

 oxygen apparatus. 



It was inevitable that a considerable difference in the amoimt of oxygen 

 consumption on fertilisation should have been observed between different 

 batches of eggs and sperm from different females and males. In some 

 individuals the generative products were naturally more ripe and in better 

 condition than in others. As the eggs and sperm for experiments of this 

 kind have to be cut out of the animals and not laid by the animals in the 

 normal manner in the sea, there is always some uncertainty as to their being 

 perfectly mature. 



The eggs can only be roughly tested by adding a little sperm to a few eggs 

 in a watch crystal and seeing how evenly and quickly fertilisation takes 

 place. As Warburg (4) remarks, it is obviously necessary in determinations of 

 this kind that fertilisation should take place in all the eggs at the same 

 moment, and that the rate of progress of this process, once it is set up in the 

 eggs, should be the same in all the eggs. These conditions are not always 

 successfully hit off in an experiment. In a certain small number of experi- 

 ments out of some 200 to 300 performed, these conditions were probably as 

 favourable as the experimental conditions would allow, and in these the 

 readings were remarkably similar. In the following section the figures of 

 three typical experiments of this kind are given. A graph of the readings is 

 shown in figs. 1, 2, and 3, where the oxygen consumption in cubic millimetres 

 is given plotted against the time in minutes. 



III. Experiments. 



Unfertilised Eggs. (20 mgrm. egg N.) 



The oxygen consumption of the unfertilised egg is so low that it is quite 

 unmeasureable with any degree of accuracy, unless a much larger number of 

 eggs is used than when a determination is made on fertilised eggs in the 

 ordinary way. Instead of using one to half a million eggs, 4 to 5 millions 

 (20 mgrm. egg nitrogen) were used in arriving at the correct estimation of the 

 respiration of the unfertilised eggs. 



The average (15 determinations) amount of oxygen taken up by 4 to 5 

 million unfertilised eggs, in 10 minutes, under the conditions of the experi- 

 ments was 7 c.mm. oxygen ; at this rate, half a million eggs (4 mgrm. of egg 

 nitrogen) would consume 1'5 c.mm. in this time. 



