THE VASCULAR CRYPTOGAMS 



2] 



divisions ; the small cells thus formed become rounded 

 and lie freely in the space enclosed by the external layer 

 (Fig. 12, C). Subsequently the external cells become 

 disorganised, their contents contributing to the nutrition 

 of the central group. The prothallus - cell, however, 

 persists all through. The round central cells are alone 

 concerned in the 

 further development. 

 When the external 

 layer becomes dis- 

 organised, its cell-walls 

 disappear and the 

 contents flow together 

 into a structureless 

 mass, in which the 

 yound cells are em- 

 bedded. In the mean- FIG. 12. Selaginclla -, germinating micro- 

 time important changes 



' c 



go On in the Contents B, more advanced stage ; c, central cells 

 nf fVoc> r>ollQ TVa which will form spermatozoids. C'.mature 



stage ; sp. m, spermatozoid mother-cells, 



large nucleus, which surrounded by cells of wall of anther- 



i T, i -i idinm. D, free spermatozoids, each with 



each cell contains, be- two dlia> ^ magnified 290 diameters ; 



COmeS Converted into #, magnified 290 diameters ; C, magni- 

 , , -, T , fied 640 diameters ; D, magnified 780 



a long, rather club- diameters. (After Belayeff.) 



shaped body, which 



has a spiral twist. At the thin end of this body there 

 is a little protoplasm, and at this point two excessively 

 fine protoplasmic threads are attached (see Fig. 12, D). 

 The whole body now constitutes a spermatozoid, and the 

 protoplasmic threads are its cilia. The cell in which a 

 spermatozoid is formed is called its mother-cell. The 

 surrounding cells having completely broken down, the 

 spermatozoid mother-cells are let loose into the water, 



