63 ELEMENTARY BIOLOGY. [CHAP. 



b. The reproductive organs. 



These are to be found by examining the under surface of 

 the prothallus with | obj. 



1. The antheridia. Most numerous near and among the 

 rootlets* 



a. Their form: small hemispherical eminences. 



b. Their structure: made up of an outer layer of 

 cells containing a few chlorophyll-granules, and 

 through which can be seen, according to the 

 stage of development, either a single central cell, 

 or a number of smaller cells (mother-cells of 

 antherozooids] resulting from its division: in the 

 latter cells, in ripe antheridia, spirally coiled 

 bodies (antherozooids} can be indistinctly seen. 



2. The antherozooids. 



Some of these are sure to be found swimming about 

 in the water if a number of ripe prothalli are examined. 



a. Small bodies, coiled like a corkscrew, thick at 

 one end, and tapering towards the other, which 

 has a number of cilia attached to it. To the 

 thicker end of the antherozooid is often attached 

 a rounded mass containing colourless granules. 



b. Treat with iodine; this stains them and stops 

 their movements, so that their form can be more 

 distinctly seen. 



3. The archegonia. Make vertical sections of the pro- 

 thallus passing through the cushion; either by simply 

 chopping down it with a razor, or holding it between 

 two pieces of carrot and cutting. Note in the 

 archegonia 



a. Their form: chimney-shaped eminences with a 

 small aperture at the apex. 



