Action of the Spermatozoon upon the Egg 237 



and that the second treatment with the hypertonic solution 

 might only be needed to create a centrosome de novo in the 

 egg. The idea was not probable, since we saw that the mem- 

 brane formation alone suffices to provide the egg with the centro- 

 somes and astrospheres necessary for cell division, as the egg 

 is able to segment if the temperature is not too high; and sec- 

 ond that it is possible to substitute for the hypertonic solution 

 the suppression of oxidations, a factor which directly sup- 

 presses the production of astrospheres. Moreover, the experi- 

 ments by Hindle have shown that the centrosomes are not 

 formed while the eggs are in the hypertonic sea-water. The 

 following observations and experiments by the writer indicate 

 that the hypertonic solution does not act in these experiments 

 by the creation of astrospheres or centrosomes. 



When we put the unfertilized eggs of S. purpuratus directly 

 into hypertonic s^a-water (without submitting them to the 

 butyric-acid treatment) and if we put them back at different 

 intervals into normal sea-water, we find that if the eggs have 

 been exposed a sufficiently long time (two hours or more) to 

 the hypertonic sea-water a number will begin to segment. 

 These eggs will often go only into the two- or four-cell stage, 

 or sometimes to the eight- or sixteen-cell stage, and then stop 

 developing. They cease to divide, and remain in the resting 

 stage.' Such eggs remain after this perfectly normal and they 

 have the appearance of small unfertilized eggs. If we wait 

 for some time, say twenty-four hours, to make sure that they 

 neither develop nor disintegrate, and add sperm, each one of 

 these blastomeres forms a tightly fitting membrane. They 

 begin to develop in a perfectly normal way and into normal 

 larvae. We are then dealing with eggs which, after having 

 been treated with hypertonic sea-water, were in possession of 

 the whole apparatus for cell division, since they actually had 



1 This phenomenon is much more common in the eggs of S. purpuratus than 

 in those of Arbacia. 



