ii8 THE LIVING CYCADS 



into contact with the extremely turgid neck cells these 

 lose so much of their contents that they appear more or 

 less shrunken. The pressure within the egg has been 

 increasing until the contents are retained only by the 

 rigidity of the turgid neck cells, and consequently even 

 a slight decrease in the turgidity of the neck cells would 

 allow the escape of a small portion of the protoplasm of 

 the upper part of the egg, together probably with some 

 gas. In this way there is formed at the apex of the egg a 

 vacuole, which may be of very short duration. We sug- 

 gest that this series of conditions would result in draw- 

 ing the sperm into the egg, the cilia merely keeping it 

 oriented, for sperms just within the egg always show the 

 apex in advance. 



While the whole sperm enters the egg, the nucleus 

 soon slips out from the protoplasmic sheath and moves 

 toward the egg nucleus, leaving the sheath with its cil- 

 iated band in the upper part of the egg. The sperm is 

 very large in proportion to the neck of the archegonium, 

 and it may be that the constriction of the sperm during 

 its entrance into the egg loosens the sheath so that the 

 nucleus slips out more easily. When more than one 

 sperm enters the egg, as is frequently the case, the 

 nucleus of the second sperm does not slip out from the 

 sheath, but the whole sperm remains intact in the upper 

 part of the egg. Doubtless the first sperm opened the 

 neck of the archegonium so that the second suffered 

 little constriction, and the protoplasmic sheath was not 

 loosened. 



The protoplasm of the sperm gradually mingles 

 with that of the upper part of the egg, and the two soon 

 become indistinguishable, but the spiral band with its 



