Metaphyta PolytricJin m. 



107 



the neck to permit of the entrance of the sperms. The 

 ovum, by transverse division, adds one more to the row of 

 canal cells. 



Notwithstanding the great apparent dissimilarity of the 

 various organs to those of Fucus, it is possible to see in the 

 venter the very much reduced cavity of a female ' concep- 

 tacle. 1 The comparison of the two cases will best be under- 

 stood by reference to fig. 36, where a diagrammatic repre- 



FIG. 38. Polytrichum commune. (Maout and Decaisne.) 



i, Theca with calyptra. 2, Calyptra removed to show operculum. 3, Operculum 

 removed. 4, Transverse section of theca. 



sentation of the two ' conceptacles ' is given showing them, 

 as it were, originating from the same thallus. It will be seen 

 that the conceptacle of the moss is simply an upraised and 

 free conceptacle of Fucus. In Fucus the contents of the 

 ovarium broke up into eight cells, all of which became ova. 

 Here seven of these cells perform a very subsidiary function, 

 namely, that of forcing the mouth of the * conceptacle ' open 

 for the entrance of the sperm. Naturally the close-fitting 

 and protecting venter and neck do away with the necessity 

 of a special protecting cell- wall or capsule for the ovum and 

 the seven modified ova, or canal cells. 



It is subsequent to fertilisation that the difficulty of 



