FERTILIZATION REACTION IN ARBACIA PUNCTULATA. 269 



quiescent in the solution alone. The percentage of membranes 

 was raised from o per cent, to 84 per cent, by increasing the 

 sperm concentration at insemination from one drop of 1 : 25 to 

 12 drops of the same suspension. The higher sperm concentra- 

 tion of this test resulted in much polyspermy. 



It would be expected that by increasing the concentration of 

 the CdCl 2 in solution, a cleavage-toxic point could be determined. 

 I was successful in this; such a concentration is I : 250, or TV 23 — . 



10. Cobalt Chloride. — When a series of tests was made to 

 establish the concentration of CoCl 2 necessary to inhibit the 

 elevation of membranes, and the concentration necessary to 

 inhibit completely the formation of the first cleavage in eggs 

 which have been inseminated in normal sea-water and transferred 

 to the solution five minutes after the insemination, it was found 

 that both are much higher that in the other metals w.th which 

 I worked. The membrane-inhibitory point was found to be 

 1 : T 373> or iV/89.245, while cleavage-toxicity occurred at 1 : 100 

 or N/6.5. As was the case with Cadmium, though not to such 

 an extent, the toxicity of even the membrane-inhibiting concen- 

 tration on eggs which had been inseminated in normal sea-water 

 and trans r erred to it, was very marked. 



Agglutination is good in the solution. The membrane- 

 inhibiting concentration makes the sperm sluggish but this 

 harmful effect is corrected by the addition, of the NaOH or a 

 drop of the concentrated egg sea-water. 



11. Mercuric Chloride. — As has already been stated above, 

 there is one metallic salt which is irregular in its behavior. This 

 is Mercuric Chloride. All the other salts with which it has been 

 possible, to work have a double effect on the eggs of Arbacia. 

 The first effect is at the weaker concentration and is on the 

 phenomenon of membrane elevation; the second effect is con- 

 stantly at a greater concentration and is dependent on the time 

 of exposure of the gametes for the intensity of its action. It 

 modifies materially the viability of the eggs and I have termed 

 it "cleavage-toxicity." The tests made with HgCU show that 

 there was no concentration which would inhibit the elevation of 

 membranes and allow cleavage if eggs were placed in it five 

 minutes after they were inseminated in normal sea-water. 



