168 EDWIN J. COHN. 



I. INTRODUCTION. 



The changes in the physiological condition of the spermatozoon, 

 from the time it is extruded fr6m the genitalia of the male until 

 it "undergoes the transformation into a nucleus" (Loeb, J., 

 I 9 I 3. P- 36) in the protoplasm of the egg are dependent in 

 rate upon environmental conditions. The germ cells of most 

 marine invertebrates are extruded into sea water, and fertiliza- 

 tion of the egg by the sperm there follows. The environment, 

 sea water or sea water modified by the excretions of the egg or 

 of the sperm- -must therefore be studied in order to understand 

 the variations in the physiological condition of spermatozoa 

 that have often been observed. 



This investigation had its beginning in an attempt to under- 

 stand seemingly contradictory effects of sea water that had con- 

 tained the eggs of the sea urchin, 1 Arbacia punctulata, upon the 

 activity, the length of life and the "fertilizing power" of the 

 spermatozoa of the same species. For interesting me in these 

 phenomena, and for invaluable aid in this attempt at their 

 solution, I am indebted to Dr. F. R. Lillie. 



The experimental work was carried on during the summers of 

 1915 and 1916 at the Marine Biological Laboratory at Woods 

 Hole, Massachusetts. During that time the behavior of the 

 germ cells of other marine invertebrates were sufficiently ob- 

 served to suggest that the relations that are hereafter reported 

 for Arbacia are not highly specific. 



MATERIAL AND METHODS. 



The sperm of the sea urchin, Arbacia punctulata, are shed from 

 the genital pores, if the peristome is cut, and the urchin placed 

 aboral side down. The sperm may then be collected in a clean 

 dry watch glass, and diluted to any concentration by the ad- 

 mixture of sea water. The concentration of the sperm suspen- 

 sion records the extent of dilution of the sperm. A one per cent, 

 suspension is one in which one drop of sperm is added to 99 drops 

 of sea water or of sea water that has suffered a definite modifica- 

 tion. 



The relative "fertilizing power" of sperm that had been sub- 



1 Such sea water is for convenience called egg water. 



