4-O2 E. E. JUST. 



hypertonic sea-water. The present study has nothing to add to 

 these and other accounts of experimental parthenogenesis in 

 echinid ova. 



Briefly, I found that among a given lot of eggs in normal sea- 

 water following exposure to hypertonic sea-water some would 

 divide and form plutei that failed to swim at the surface, and that 

 among those eggs that did not show cleavage were some that 

 appeared unaffected by the exposure, while others formed monas- 

 ters. Prolonged exposure was found to induce numerous cytas- 

 ters. The egg nucleus, so far as I could determine, undergoes no 

 increase in size while the eggs are in the hypertonic sea-water. I 

 was likewise able to confirm Moore's finding, namely, that these 

 eggs in sea-water after exposure to hypertonic sea-water give off 

 fertilizin. These eggs never form membranes, as is well known. 



II. 



Moore has shown in an important contribution to the analysis 

 of fertilization that the eggs of Arbacia inseminated immediately 

 on return to sea-water after exposure to hypertonic sea-water (in 

 the proportion of 8 parts 2 l / 2 M NaCl to 50 parts sea-water) 

 develop for the most part in greater numbers than similarly ex- 

 posed eggs without insemination. These inseminated eggs pro- 

 duce membranes comparable to those found on normally fertilized 

 eggs. Cytological study revealed that sperm penetrate these eggs 

 treated with hypertonic sea-water, but play no active role. 



For the most part my findings agree with those of Moore. 

 Since, however, the object of my study was somewhat different 

 from his, my methods differed. This difference in method may 

 well account for those of my results that are at variance with his. 



In his experiments Moore gave the eggs graded treatment with 

 hypertonic sea-water and inseminated them immediately on return 

 to sea-water. In my experiments, since the primary object was to 

 learn the fertilization capacity of the egg of Arbacia whose nucleus, 

 , having broken down, was thus in one or another stage of mitosis, 

 I inseminated the eggs at intervals following their return to normal 

 sea-water. It may be that the egg should lie for a time in normal 

 sea-water, subsequent to exposure to hypertonic sea-water, before 

 insemination in order to regain its equilibrium with the normal 



