23 



E. Changes In the nuclear cup* 



When solutions with a lower osmotic concentration than 

 sea-water come in contact with the nuclear or protoplasmic cup 

 it becomes thicker and the pseudopodia &re withdrawn so that 

 the outline of the sperm, viewed from the top or bottom of 

 the cup, is circular instead of star-shaped. The disappear- 

 ance of the pseudopodia proceeds by a swelling at the base 

 while the outer portion tapers very gradually to an extremely 

 fine point. Compare Fig* 62 with 63 and 65. As the base 

 widens out still father the rays are reduced to a very fine 

 thread which either breaks off or is contracted into the body. 

 When the pseudopodia break loose from their attachment the 

 whole sperm is apt to move suddenly and then be borne away if 

 there are any currents in the containing fluid. This sudden 

 movement probably results from some of the pseudopodia break- 

 ing loose slightly before the others. This rather than the 

 explosion of the capsule may be the explanation of the "spring- 

 ing of the sperm" discussed by Kolteoff '06. This rounding 

 up of the protoplasmic portion of the sperm is apt to be com- 

 pleted before any change takes place In the capsule. Some- 

 times however the capsule may be completely changed before 

 the disappearance of the pseudopodia. Probably In rapid ex- 

 plosion the two take place simultaneously. 



8. Changes in the capsule . 



For the Interpretation of the entrance of the sperm into 

 the egg the transformation of the capsule is much more import- 



