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 Selaginella, while in the 

 Ferns and Horsetails the cilia are 

 much more numerous. In Pellia 

 the body of the spermatozoid is 

 spirally coiled, with the cilia attached 

 just behind the thin end, which 

 keeps in front while the spermato- 

 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 



FIG. 53. Single sperm- 

 atozoid of Pellia, 

 showing the spirally 

 coiled body and the 

 two long cilia. Mag- 

 nified 1225. (After 

 Guignard.) 



