PHYSICS OF SEGMENTATION. 99 



tion of artificial development by lowering the temperature is 

 brought about by an extraction of water from the protoplasm, 

 just as if the eggs had been placed in a solution of higher os- 

 motic pressure than that of the sea water," l though no explana- 

 tion of the reason for this is offered. A suggestion as to this is 

 however made by Mathews in his comments on the fourth 

 method, that " the getting of parthenogenesis by agitation may 

 be due to a dissolution of the nuclear membrane, since the cen- 

 trosome originates close to the nucleus, or it may cause the eggs 

 to lose water like the cells of sensitive plants. The loss of water 

 could be caused only by lowering the osmotic pressure in the 

 cell, and this by decreasing the number of molecules in the cell ; 

 and this in turn by synthetic processes." 



In other forms artificial parthenogenesis may be obtained by 

 similar or slightly different methods ; c. g., in Arbacia by osmotic 

 pressure, 50 c.c. :2 ^- TV MgG 2 or NaCl + 50 c.c. sea water, 3 and 

 at least a segmentation by lack of oxygen, by heat, or by ex- 

 posure to alcohol, chloroform, or ether; 4 in Chcetopterus likewise 

 by the use of KG, KNO 3 , K 2 SO 4 (2^4 N+ 100 c.c. sea water), 

 NaCl, MgCl 2 , CaCl 2 and sugar, 5 in Amphitntns by Ca(NO 3 ) 5 

 (2 c.c. N -\- 99 c.c. sea water) ;'' in Nereis by osmotic pressure, 

 (20 c.c. 2^/2 N KG + 80 c.c. sea water, 30 minutes), 6 in 

 Podarke obscura by use of the same solution. 7 As theories and 

 interpretations of the results obtained by these factual methods, 

 we find in addition to those already cited the following, which are 

 quoted in abstract : 



" All that the spermatozoon needs to carry into the egg for 

 the process of fertilization are ions, Mg, K, HO or others, to 

 supplement the lack of the one or counteract the effects of the 

 other class of ions in the sea water, or both. The ions and not 

 the nucleins in the spermatozoon are essential to the process of 



1 Greeley, loc. cit. 

 2 Mathews, loc. cit. 



3 Loeb, J., Am. Jon?: of Physiology, Vol. III., Nos. III. and IX. and Vol. IV., 

 IV. 



4 Mathews, A. P., Am. Jour, of Physiology, IV., VII. 

 5 Loeb, J., Am. Jour, of Physiology, IV., IX. 

 6 Fischer, M., Am. Jour, of Physiology, VII., III. 

 7 Treadwell, BIOLOGICAL BULLETIN, III., 5. 



