ELECTRICAL CONDUCTIV^ITY OF FKRTILIZED AND UNFERTILIZED EGGS. 53 



due to the direct effects of fertilization. The following alternative sugges- 

 tions might be offered : — ' 



1. That the changes are due to the injurious effect of the current upon 

 the eggs. For this, however, evidence is entirely unavailable. Eggs 

 upon which definite and prolonged experiments had been made on June 

 18th were transferred to a bowl of clean sea-water, all the eggs divided 

 normally, and all gave healthy larvae. Some of these early plutei were 

 placed in a sterilized jar and fed with a pure diatom culture ; on July 11th 

 the plutei were large and healthy. They had developed at a normal rate, 

 and a definite Echinus rudiment was visible. Several such observations 

 of the development of eggs whose resistance had been measured were kept, 

 and in each case the development was perfectly healthy and normal.* 

 It is therefore, I think, safe to conclude that the eggs were unaffected 

 by the passage of the current used in these experiments. 



2. That the changes are due to experimental error in returning the eggs 

 to the same volume. To determine the degree of error due to such a 

 source, I made successive determinations on the resistance of the same 

 lot of unfertilized eggs. I found that the variation of the readings never 

 exceeded 2% of the total resistance (in many cases successive readings 

 were identical). Now" such a difference might perhaps explain experi- 

 ments in which the total resistance is belov/ 20 ohms, but is quite in- 

 adequate for the much larger differences which were regularly observed 

 for eggs compacted to give higher resistances. 



3. That the decrease in resistance of the eggs subsequent to fertilization 

 is due to the presence of the fertilization membrane and not to the 

 substance of the egg itself. It cannot, however, be suggested that the 

 spaces between the egg are enlarged by the membrane, for the unfertilized 

 eggs are not crushed during the experiments, and any crushing undergone 

 by the fertilized eggs is at the expense of the membrane and not of the egg. 

 If the eggs are closely compacted after fertilization it is almost invariably 

 found that either the membranes are much wrinkled or are removed 

 entirely from the egg on the addition of fresh sea-water. Again, during 

 the course of the experiments it was found that the fertilization membranes 

 in some batches of eggs were never pushed far out from the egg, but 



* In the case of Echiiius miliaris jilutei, which according to Shearer, De Morgan and 

 Fuchs fail to develop their green pigment if unhealthy, ray cultures invariably possessed 

 this character and were, in the opinion of Dr. Shearer, perfectlj' healthy. (Most of the 

 cultures were discarded as soon as the Echinus rudiment had reached considerable size, but 

 in two cultures which were preserved the larvpe underwent perfectly typical metamor- 

 phosis — a little more than a month after fertilization, which is in agreement with the rate 

 of development of tlie egg under normal conditions.) 



