FERTILIZATION REACTION IN ARBACIA PUNCTULATA. 



263 



copper salts of the fertilization reaction of Arbacia and found 

 that there was a membrane-inhibiting point at I : 500,000 He 

 also determined the cleavage-toxic concentration as 1 : 62,500. 

 A repetition of this work confirmed the determinations that he 

 made save that for one of the females employed it was found 

 necessary to use a concentration of 1 : 37,500 CuCl 2 to completely 

 inhibit cleavage. As has been stated above, the cleavage-toxic 

 concentration varies somewhat, both for the eggs of different 

 females and for the different physiological conditions existing in 

 the eggs of the same female. 



3. Zinc Chloride. — Zinc, it will be recalled, is one of the metals 

 which formed such a precipitate that a cleavage-toxic concentra- 

 tion could not be determined. In the weaker solution necessary 

 to completely inhibit the formation of membranes, however, the 

 salt could be used with little difficulty. The usual series of 

 experiments for the determination of this point was set up. 

 The result of such an experiment may be found in Table I la. 



Table I la. 



Concentration of ZnCh in Sea-water. 



Per Cent. 

 Membranes. 



Per Cent. 

 2 Cell. 



Per Cent. 



A Cell. 



I : 250,000 



1 : 200,000 



1 : 175,000 



1 : 150,000 



1 : 125,000 



Inseminated control in sea-water. . . . 

 Uninseminated control in sea-water. . 



96 

 6 

 o 

 o 

 o 



96 



o 



76 



5 



o 



96 



Present. 



96 



Test of membrane-inhibition of ZnCh. July 5, '22. Q C. Eggs and sperm 

 fresh. Insemination 1 : 25 : 7.5. Exp. 2 : 30 P.M. Insemination immediate. 

 All membranes narrow. 



Table 116 is a record of the viability of eggs which were in- 

 seminated in normal sea-water and transferred to the ZnCl 2 

 solution at intervals as indicated. It will be noted that when 

 good membranes are raised, the toxicity of the membrane- 

 inhibiting concentration on cleavage is not very marked. When 

 narrow membranes have been raised the viability is much poorer. 



4. Lanthanum Chloride. — Gray ('15) found that cerous chloride 

 in a very weak concentration, would aggregate the sperm of 

 Arbacia. He also found that by the addition of a small amount 



