58 J. GRAY. 



are so crowded that they develop at a rate different from that of control 

 eggs kept in abundance of water. The change in rate of development 

 varies with different batches of eggs and with their degree of concentration. 

 Hence it is impossible by this method to determine the conductivity of 

 normal eggs (i.e. eggs developing at a normal rate) at any stated moment. 

 As, however, the development of the eggs in the conductivity tube is only 

 abnormal in respect to time (i.e. the cleavage divisions are quite normal 

 but occur at a varying time after those in a control), it may be concluded 

 that the sequence of events in the two cases is the same. 



A more important limitation lies in the fact that the resistance can 

 only be determined by concentration of the eggs. We may conclude 

 that when the eggs are concentrated at the bottom of the tube, their 

 development very quickly becomes delayed until the return of normal 

 conditions ; hence it is not possible to take a large number of readings 

 during one experiment. 



These two factors would account for the variation found in curves 

 obtained from the individual experiments. For example, most of them 

 show the same maximum and minimum points during the first hour of 

 development, but corresponding points on different curves do not agree 

 in point of time. Again, it is almost certain that the primary rise in 

 conductivity due to the entrance of the sperm, lasts only for some fifteen 

 minutes or less ; if therefore it is found impossible (for technical reasons) 

 to determine the resistance of the fertilized eggs during this period, the 

 pronounced minimal point which exists during the first ten minutes of 

 development is entirely lost, and the curve differs radically in appearance 

 from the normal. Owing to the rapid rate in the rise and fall of the 

 conductivity at the commencement of development the exact time 

 at which the resistance is determined is of considerable importance. For 

 example, one experiment gave the following data : — 



The resistance of eggs 3 mins. after fertilization was 10" 5 ohms less 



than that of the unfertilized eggs. 

 J, ,, ,, 9 ,, after fer. was 12.5 ohms less 



^'^ ^ 



3 J 55 55 -'•"-' 55 55 55 " 55 55 



35 55 35 ■"" 55 55 55 '"' 55 55 



In other words, the conductivity of the eggs has undergone profound 

 changes within 13 minutes. It is therefore necessary to discover the 

 position of the maximum and minimum points with considerable accuracy 

 before any quantitative value can be ascribed to the changes in con- 

 ductivity which take place during the development of the normal egg. 



