PTERIDOPHYTA AQ] 
spermatozoid, and the fertilized egg develops into a sporophyte, 
as in other pteridophytes. In some cases archegonia may be pro- 
duced, the eggs may be fertilized, and sporophytes may begin to 
develop before the spores are shed. 
Specialization of sporangia. The sporangia of Selaginella show 
greater specialization than do those of typical ferns in that they 

Fig. 449. Gametophytes of Selaginella 
Left, section of a female prothallus; the megaspore wall is shown in black ; note 
the archegonium projecting from the upper surface of the prothallus (redrawn 
after Miss Lyons). Upper right, male gametophyte of Selaginelia; note that it 
consists of asingle prothallial celland asingleantheridium (redrawn after Belajeff). 
Lower right, spermatozoids of Selaginella (redrawn after Belajeff) 
are differentiated into megasporangia and microsporangia. The 
differentiation of the sporangia and spores of Sedaginella has been 
accompanied by a decrease in size and a loss of independence in 
the prothalli. “Chey are small and are dependent for development 
on food stored by the sporophyte in the spore. 
The differentiation of spores into megaspores and microspores, 
and their dependence on the sporophyte, has certain obvious 
advantages. The delicate prothalli of ferns do not appear to be 
very well suited to life on dry land, as they require a considerable 
