314 WILLIAM SEIFRIZ. 



were normal, part of each lot used was kept and tested for 

 fertility. 



The response to dissection of ripe unfertilized ova may vary 

 from immediate disintegration to the toleration of two severances. 

 Many eggs are very easily pinched in half by two needles rapidly 

 approaching from opposite sides. The halves frequently round 

 up into perfect spheres which can be again severed to form smaller 

 protoplasmic droplets. While some eggs will show but slight if 

 any increase in viscosity after many minutes of slow movement 

 of the needles, others will suffer little or no dissection before 

 gelating or completely disintegrating. Mere puncturing of the 

 egg will often cause gelation. Thus does the ripe egg exhibit 

 in one instance great sensitiveness and in another apparent 

 indifference to stimulus. 



This variability is carried even to parts of the same egg. 

 One half of a severed ovum may gelate immediately without 

 forming a wall over the torn surface, while the other half tolerates 

 still another severance before gelating and thus losing the ca- 

 pacity for wall-formation. The presence of the nucleus in one 

 half of the egg may be responsible for this difference in behavior 

 (Townsend, 1897), although frequently both halves develop 

 enclosing walls. 



The protoplasm of the living ovum is at all times non-miscible 

 in sea-water. This is to be expected if the capacity for wall- 

 formation persists as long as the protoplasm is alive. In no 

 instance of eggs examined in the various stages of ripening, w T hile 

 mature, and in the brief period following fertilization when the 

 wall was still penetrable, was the plasma found to pour out and 

 mix with the surrounding water. 



The Unicellular Embryo. 



Fertilization in Fucus is readily accomplished if active sperm 

 are placed on a slide with mature ova. 



Half an hour after application of the sperm the protoplasm 

 of the fertilized ovum is found to be still quite viscous. A little 

 later it becomes more liquid, for it readily oozes out of a puncture. 

 Further development of the unicellular embryo shows a con- 

 tinued decrease in protoplasmic density. 



