ON EGGS OF MARINE ANIMALS 43 



microscope in order to ascertain whether or not the jelly has 

 been removed. Eggs with jelly do not touch each other, eggs 

 without jelly do. Also, if the eggs be placed in a suspension of 

 Chinese ink, made by grinding up the end of a stick of ink in 

 sea-water, the eggs without jelly are enclosed by particles of 

 ink, whilst eggs with jelly are surrounded by a clear space, the 

 jelly hull. 



On the whole, I regard removal of the egg-jelly by means of 

 acid sea-water as unsatisfactory. In order to be sure of success 

 one must use several concentrations because of the individual 

 and seasonal variations of the eggs. Under the m.ost favorable 

 conditions the washing subsequent to acid treatment is laborious 

 and time-consuming if one needs a large number of eggs. 



Shaking will remove the e^g jelly, but in my experience is 

 uncertain when the eggs are at their seasonal optimum. Toward 

 the end of the breeding season the jelly is more easily removed; 

 indeed, eggs then frequently lose their jelly on standing in normal 

 sea-water without any treatment. Nor can I recommend the 

 KCN method of Vies. 



I find that the simplest and most eflFective method of remov- 

 ing the jelly from eggs of echinids is to put them through bolting 

 silk. In this way the eggs are in no wise impaired, as can be 

 demonstrated by the fact that their membrane-separation is of 

 the same rate, quality, and per cent, as that of eggs from the 

 same female which possess jelly hulls. One merely pours the 

 eggs on to the wetted bolting silk stretched over a finger bowl 

 containing sea-water. There is only one precaution: 07ie must 

 not use pressure — e.g., by pouring eggs from a height greater than 

 three or four centimeters. Eggs examined under the microscope 

 in a suspension of Chinese ink in sea-water are found free of 

 jelly. If some eggs still possess jelly they are put through the 

 bolting silk again. I have used this method for several years 

 now. After rather tedious comparisons with the other methods 

 named, I can safely say that it is the best. 



Methods for Removing the Vitelline Membrane 

 FROM Inseminated Echinid Eggs 



A great deal of experimental work has been done on echinid 

 ova whose vitelline membranes have been removed after their 



