PTERIDOPHYTA 



243 



of the sperm-cells, a peculiar body, the blepharoplast, becomes visible. 

 This closely resembles the centrosomes found in some plants, and is 

 sometimes considered to be of the same nature. After the final divi- 

 sion, each sperm-cell contains a single blepharoplast lying close to 

 the nucleus, in which no nucleolus can be seen. 



The nucleus becomes elongated, and assumes a crescent form, 

 gradually becoming longer and assuming the coiled form of the per- 

 fect spermatozoid, most of which is derived from the nucleus of the 

 sperm-cell. The blepharoplast also elongates, and is closely applied 

 to the nucleus, beyond which it projects as the anterior cilia-bearing 

 end of the spermatozoid. The cilia are, apparently, developed 

 exclusively from the blepharoplast. 



B 



C 



FIG. 208. Marsilia vestita. Development of the spermatozoid (X 1500) ; 6, blepha- 

 roplast. A-C, last division, preliminary to the formation of the spermatozoid. 

 L-F, development of the spermatozoid ; n, nucleus of sperm-cell. (After SHAW.) 



Fertilization. As in all other Archegoniates, the opening of the 

 reproductive organs is dependent upon the access of water, and is 

 accomplished exactly as in the Bryophytes. In the matter ejected 

 from the open archegonium of various Ferns, it has been shown that 

 malic acid is present, which exercises a strong attraction upon the 

 spermatozoids. On reaching the open archegonium, the spermato- 

 zoids crowd into its neck, often completely choking it. The mucilage 

 filling the neck retards their movements somewhat, and detaches the 

 vesicle attached to the hinder coil of the active spermatozoid. The 

 spermatozoid moves slowly by a spiral motion, through the narrow 

 neck-canal, until it reaches the central cavity in which is contained 

 the egg. The first spermatozoid to enter penetrates at once into the 



egg- 



The fusion of the spermatozoid with the egg-nucleus (Fig. 215) 

 is slow in the common Ferns, where it has been most completely 



