240 E. G. SPAULDING. 



and in the number segmented at all cleavages. No period of 

 susceptibility was indicated. This acceleration effect might 

 according to the views above discussed be ascribed to the so- 

 called "overbalancing effect" of the trivalent radical, but the 

 experiment was not repeated because of lack of time. 



SUMMARY AND CONCLUSIONS. 



1. There is a pronounced rise in iunn unity of fertilized sea- 

 urchin eggs to ether up to eithery/^Y before or the beginning of 

 segmentation ; the exact point is impossible to determine owing 

 to the unevenness of the cleavage. A sharp decrease then occurs, 

 followed by a sharp rise toward the end of the cleavage. A repe- 

 tition of this occurs at the second segmentation. 



2. Similar changes are found resulting from the use of HC1, 

 KC1, and NaCl with the difference that the fall in immunity 

 comes somewhat earlier with KC1 than with HC1 and with this 

 than with ether. All of these differ therefore from Lyon's inter- 

 pretation of the susceptible points with KNC as occurring "after 

 division," nor is a 15' period found, although with HC1 there is 

 a fall in immunity at 30' after fertilization. 



3. The marked decrease in immunity " at cleavage" caused 

 by the four agents employed seems to be explainable on the 

 basis that all, in one way or another, augment beyond a certain 

 point the increase in osmotic pressure normally necessary for 

 cleavage. The results obtained seem therefore to be confirma- 

 tory of the position presented by the author elsewhere * that 

 cleavage is due to the equalization (Ausgleichung und Umfor- 

 mung) of an uncompensated potential difference between osmotic 

 pressure and surface tension, accompanied by electronic phe- 

 nomena which cause constriction. 



The author wishes to acknowledge his appreciation of the 

 many opportunities offered him by the Laboratory and of the 



kind advice and suggestions of Dr. Mathews. 



COLLEGE OF THE CITY OF NEW YORK, 



DEPARTMENT OF PHILOSOPHY, January, 1904. 



1 UIOLOCICAL IJri.i.ETiN, February, 1904. 



