280 THE BIOLOGY OP THE PLAiTT 



spermatozoid. If the antheridium be quite ma- 

 ture, some of the spermatozoids may be seen 

 swimming about in the water. If so, examine 

 them carefully. What is their shape ? Do they 

 have the same diameter at each end? At their 

 anterior end look for two long flagella. If the 

 structure of the spermatozoid is not plain, apply 

 dilute iodine. How do the spermatozoids move ? 

 For how long is their motion kept up ? Look for 

 antheridia in different stages of development. 

 Study and draw the stages found. 

 Make drawings showing : (1) the antheridium as seen 

 from the outside ; (2) a shield seen from without ; (3) a 

 shield with manubrium, etc. ; (4) a spermatozoid. 



2. The oogonia. — Compare these as regards posi- 

 tion, shape, size, color, etc., with the antheridia. 

 Do you find any constant relation existing be- 

 tween the position of the antheridia and that of 

 the oogonia ? Is the oogonium borne upon a stalk ? 

 ISTote its outer covering of spirally twisted cells. 

 Do these run as single cells from the base to the 

 apex of the oogonium? How many are there? 

 Note the crown, consisting of small cells. What 

 is their number ? What is their position with re- 

 gard to the spiral cells ? Note the central cell or 

 oosphere of the oogonium. How does it com- 

 pare in size with the other cells? What does it 

 contain? Certain points in the structure of the 

 oogonium may be found to be more easily seen 

 in specimens preserved in chromic acid and exam- 

 ined in glycerine. 

 Draw an oogonium, showing its entire structure. 



Examine a number of specimens for oogonia in 



