26 



SEX AND HEREDITY 



a nucleated primordial cell ; but it is much larger than 

 the spermatozoid, and is not motile. It lies protected in 

 a flask-like sheath called an archegonium, while at maturity 

 the neck of the flask is open (Fig. 13, B). For the 



B 



A 



FIG. 14. 



Fertilization in a Fern (Onoclea). A=a vertical section through an open arche- 

 gonium, probably within ten minutes after the entrance of the first spermatozoid. 

 ( x 500.) B a vertical section of the venter of an archegonium containing sperma- 

 tozoids, and-the collapsed egg with a spermatozoid within its nucleus. Thirty 

 minutes. ( x 1200. After Shaw.) 



archegonium also ruptures by swelling with water, and 

 a channel of access to the egg is thus provided. The 

 spermatozoids enter that channel in numbers (Fig. 14, A), 

 and one of them finally penetrates the egg (Fig. 14, B) . Its 

 nucleus, still preserving the spiral form, may even be found 

 embedded in the nucleus of the egg (Fig. 14 bis). But 

 finally the two nuclei coalesce completely. The two 



