426 FERNS LESS. 



On the lower surface of the prothallus gonads (E, spy^ ovy) 

 are developed, resembling in their essential features those of 

 mosses. The spermaries (spy) make their appearance first, 

 being frequently found on very young prothalli. One of the 

 lower cells forms a projection which becomes divided off by 

 a septum : further division takes place, resulting in the 

 differentiation (F) of an outer layer of cells forming the wall 

 of the spermary, and of an internal mass of sperm-mother- 

 cells in each of which a sperm is produced. The sperm (G) 

 is a corkscrew-like body, probably formed from the nucleus 

 of the cell, bearing at its narrow end a number of cilia which 

 appear to originate from the protoplasm. To the thick end 

 is often attached a globular body, also arising from the proto- 

 plasm of the mother-cell ; this is finally detached. 



The ovaries (E and H, ovy) are not usually formed until 

 the prothallus has attained a considerable size. Each arises, 

 like a spermary, from a single cell cut off by a septum from 

 one of the lower cells of the prothallus : the cell divides and 

 forms a structure resembling in general characters the ovary 

 of a moss (see Fig. 109, B, p. 406), except that the venter (H, 

 v) is sunk in the prothallus, and is therefore a less distinct 

 structure than in the lower type. As in mosses, also, an 

 axial row of cells is early distinguished from those forming 

 the wall of the ovary : the proximal of these becomes the 

 ovum (ov), the others are the canal-cells (en. c\ which are 

 converted into mucilage, and by their expansion force open 

 the neck and make a clear passage for the sperm. 



The sperms swarm round the aperture of the ovary and 

 make their way down the canal, one of them finally conju- 

 gating with the ovum and converting it into an oosperm. 



The early stages in the development of the embryo 

 remind us, in their general features, of what we found to 

 occur in mosses (p. 405). The oosperm first divides by a 



