116 STRUCTURAL BOTANY 



antheridia of Ferns, though there are some differences 

 in the details of development as well as in size. 



Each of the numerous cells of the central mass of 

 tissue produces a single spermatozoid, just as in Vascular 

 Cryptogams ; the development is also just the same, 



for the body of the spermatozoid 

 arises almost entirely from the 

 nucleus, while the cilia, which are 

 here two in number, are derived 

 from the protoplasm. The presence 

 of two cilia only is constant through- 

 out the Liverworts and Mosses. 

 Among Vascular Cryptogams we 

 find this number in the spermatozoids 

 of the Club Moss Class, as repre- 

 sented by Selaginetta, while in the 

 Ferns and Horsetails the cilia are 



FIG 53. -Single sperm- m h more numer0 us. In Pellia 



atozoid oi Pelha, 



showing the spirally the body of the spermatozoid is 



u'X41ma a " <PiMy Boiled, with the cilia attached 

 nified 1225. (After just behind the thin end, which 



keeps in front while the sperrnato- 

 zoid is swimming (Fig. 53). Here also a little bladder, 

 formed from the remains of the protoplasm and nucleus, 

 hangs on to the spermatozoid when it is first set free. 



b. The Archegonia 



The female organs, which here, as in the Vascular 

 Cryptogams, bear the name of archegonia, arise in large 

 numbers just behind the growing-points of the older 

 thalli on the upper side. The thallus always thickens 

 where they are formed. The thickened part comes to a 

 sudden end towards the margin of the prothallus, and 



