17 L. V. HEILBRUXX. 



grees, and were exposed 2, 4, 6, 8 minutes. In experiment c, 

 eggs were dropped into sea-water heated to 37.5 degrees and 

 kept at this temperature on a waterbath; the eggs were ex- 

 posed 3^ minutes. In no case could any membrane elevation 

 be observed, but the vitelline membrane did appear to be slightly 

 swollen after the heat treatment. 



Alkalis. If alkali is added to sea-water, the resultant pre- 

 cipitation of magnesium salts tend to convert the sea-water 

 into a solution containing little else than sodium salts. No 

 doubt this fact alone is of significance. It is probable, however, 

 that there is a more specific action of the alkali. As was shown 

 in a previous discussion (p. 151), alkali apparently is able to 

 liquefy the vitelline membrane. It is doubtful if any observer 

 has actually obtained membrane elevation with NaOH or KOH. 

 Certainly it does not occur when the eggs are left in the alkaline 

 solution. 



Butyric Acid. This famous method is one of the best for 

 artificial membrane elevation. Loeb used it originally on 

 Strongylocentrotus eggs, employing a concentration of 50 c.c. 

 sea- water plus 2.8 c.c. N/io butyric acid and exposing the eggs 

 1^-3 minutes. In his recent book, he applies the method to 

 Arbacia eggs reducing the concentration of acid slightly (50 c.c. 

 sea-water plus 2.0 c.c. n/io butyric), but retaining the same 

 time of exposure. He says that the eggs do not form a conspic- 

 uous fertilization membrane, but only a "fine gelatinous layer 

 which was not easily visible." This is evidently a membrane 

 swelling and not an elevated membrane. For the benefit of 

 workers in the field, I mention a slight modification in the method, 

 by which true elevated membranes may be obtained for Arbacia 

 eggs. Instead of 1^-3 minute exposures, a \ minute exposure 

 was found very effective, and over ninety per cent, of elevated 

 membrane could regularly be obtained if the eggs were well 

 washed and in good condition. The concentration used was 

 the original one of Loeb's, 50 c.c. sea-water plus 2.8 c.c. N/io 

 butyric; slight variations are however immaterial. Although 

 eggs exposed I minute often showed membrane elevation, no 

 elevation was found to occur on longer exposure. Instead the 

 membrane in every case appeared swollen, the amount of swelling 

 increasing with the length of exposure. 



