286 



CARL R. MOORE. 



had been initiated by an exposure to hypertonic sea-water, could 

 yet be fertilized, produce fertilization membranes and develop 

 into swimming larvae, he was anxious to know if fertilization 

 was prevented by failure of the sperm to enter or whether the 

 individual blastomeres the products of the first cleavage of an 

 egg had developed an immunity to the latent effects of a 

 spermatozoon. 



It is obvious that to determine this point from cytological 

 preparations a pure culture of the first two blastomeres was 

 highly desirable; and with considerable difficulty some two 

 hundred and fifty or three hundred eggs that had segmented 

 but once were isolated from lots of eggs that had been subjected 

 to the weaker hypertonic solution. This pure culture of approxi- 



FIG. 5. X 3,ooo. Section of a quarter egg showing the presence of sperm 

 nuclei. Weaker hypertonic solution, 30 to 40 minutes; .egg segmented once, 

 isolated, each blastomere segmented again. Killed 20 minutes after insemination. 



mately five hundred half-eggs was heavily inseminated, allowed 

 to stand for twenty minutes and preserved in Boveri's picro- 

 acetic acid. A very few of these blastomeres had divided again 

 into two daughter blastomeres (quarter-eggs) before the lot was 

 inseminated, but every egg was isolated from the mass culture 

 into a pure culture while in the two-celled stage. 1 



Microscopical sections of these half-eggs prove to us beyond 



1 As a definite membrane was not produced by the egg following the hypertonic 

 treatment the blastomeres became entirely separated from each other in the pure 

 culture. All were half-eggs when isolated. 



