CYCADALES 149 



mexicana. In these four forms the entire sperm enters the egg, -but 

 the nucleus soon sHps out from the cytoplasmic sheath, and leaving 

 it with its ciliated band in the upper part of the egg moves toward 



Fig. 176. — Dioon edule: upper part of ovule at time of fertilization, showing 

 integument, nucellus, and both male and female gametophytes; reconstructed from 

 sections of several ovules. — After Chamberlain (73). 



the egg nucleus. The ciliated band was observed by Lang (29) 

 in the upper part of the egg of Stangeria, so that in this form also it 

 is evident that the sperms are motile and that the whole sperm enters 

 the egg. The sperm nucleus is much smaller than that of the egg,* 

 and it penetrates some distance into the egg nucleus before the bound- 



