430 



SCIENCE 



[N. S. Vol. XXVI. No. 666 



by the fatty acid. To cause the membrane 

 form.atioii it was necessary to put the un- 

 fertilized eggs at 15° C. for from 1-j to 2^ 

 minutes into a mixture of 50 c.c. sea-water 

 plus 2.8 c.c. N/10 butyric acid (or any 

 other monobasic fatty acid). If the eggs 

 were taken a little too early from the solu- 

 tion, after about eighty seconds, only part 

 of the eggs formed membranes after being 

 transferred to normal sea-water. If these 

 eggs were afterwards treated for from 30 

 to 50 minutes with hypertonic sea-water, 

 only those eggs developed into larva? which 

 had formed the membrane. A further 

 proof lies in the following data. In 1887 

 0. and R. Hertwig published the fact that 

 if chloroform is dissolved in sea-water the 

 sea-urchin eggs may form membranes in 

 such sea-water, and Herbst showed in 1893 

 that benzol, toluol, xylol, act in the same 

 way. I suspected that all fat solvents 

 have the same effect, and an experiment 

 with amylen confirmed this expectation. 

 If the membrane formation is called forth 

 in the egg of Strongylocentrotus purpura- 

 tus with any of these fat solvents and the 

 eggs are aftei'wards treated for from 30 

 to 50 minutes with hypertonic sea-M'ater 

 they will develop into larvae. It is, how- 

 ever, important to realize that these fat 

 solvents cause cytolysis of the eggs, unless 

 the latter are transferred very rapidly to 

 normal sea-water. On acco^^nt of this 

 cytolytic effect it is preferable for prac- 

 tical purposes to cause the membrane 

 formation by a fatty acid. 



It is therefore obvious that we are now 

 in possession of a method which allows us 

 to imitate more completely the effects of 

 the spermatozoon than the previous purely 

 osmotic method. My attention was again 

 directed towards the fact that the purely 

 osmotic method gave unreliable results with 

 the eggs of the Californian Strongylo- 

 centrotus, while it gave better results with 

 the eggs of the eastern Arhacia. Experi- 



ments on the effect of the alkalinity of the 

 sea-water upon segmentation indicated 

 that the sea-water in the laboratory at 

 Woods Hole is considerably more alkaline 

 than that used by me in Pacific Grove. It 

 occurred to me whether this difference 

 might have something to do with the dif- 

 ference in the result of the osmotic method 

 in both places. This suggestion proved 

 correct. It was found that a neutral 

 hypertonic solution with a concentration 

 of hydroxyl ions of 10"'- or 10"° normal, as 

 a rule does not cause the development of 

 the unfertilized egg of Strongylocentrotus, 

 no matter how high the osmotic pressure 

 is; but that with a sufficiently high con- 

 centration of hydroxyl ions a compara- 

 tively small increase in the osmotic pres- 

 sure of the sea-water is sufficient to cause 

 the unfertilized eggs of Strongylocentrotus 

 to develop into larvffi. It was, moreover, 

 found that the minimal concentration of 

 hydroxyl ions in the hypertonic solution 

 necessary to call forth the development of 

 unfertilized eggs differs considerably for 

 the eggs of different females. For the 

 egg's of some females this minimal concen- 

 tration was as low as that found in the 

 sea-water at Pacific Grove, namely, between 

 10"" and 10"^ normal, but as a rule a 

 higher concentration of hydroxyl ions was 

 required. It is possible to obtain good and 

 constant results with the purelj^ osmotic 

 method in Strongylocentrotus if only the 

 concentration of the hydroxyl ions in the 

 hypertonic solution is sufficiently raised 

 through the addition of NaHO. In cases 

 in which the eggs of Strongylocentrotus 

 will not develop into larv?e when put for 

 about two hours at 15° C. into a mixture 

 of 50 c.c. sea-water plus 8 c.c. 2iN NaCl 

 they will develop when about 1.5 c.c. iV/10 

 NaHO is added to this solution. 



The apparently purely osmotic method, 

 therefore, turns out to be composed of two 

 agencies, one being the increased osmotic 



