94 SEX IN MICROORGANISMS 



parvulum var. ?mcropus (Kiitz.) CL, G. tenellwn Kiitz. (?), Libelliis 

 constrictus (Ehr.) DeT. (?), Navicida crucigera (W. Sm.) CI., N. 

 cuspidata var. avibigiia (Ehr.) CL, N. dire eta Ralfs., N. firma Kiitz. 

 (?), N. pygmaea Kiitz., N. ramossissima (Ag.) CL, N. scopzdorwn 

 Breb., N. subtilis (Greg.) Ralfs., N. viridula Kiitz., Niediuvi affijie 

 var. aviphirbyuch'iis (Ehr.) CL (?), Nitzschia hybrida Grun., N. 

 lofigissmm (Breb.) Ralfs., N. siginoidea (Ehr.) W. Sm., N. subtilis 

 Kiitz., Finnularia gibba Ehr., P. hemiptera (Kiitz.) CL, F. stauroptera 

 Grun. (?), P. viridis (Nitz.) Ehr., Rhoicosphenia ciirvata (Kiitz.) 

 Grun., Schizonevia laczistre Ag., Stauro7ieis phoenicenteron (Nitz.) 

 Ehr. (?). 



(3) One mother cell produces two wandering gametes, and one 

 mother cell produces two passive gametes. The apical axes of the 

 auxospores are parallel to those of the mother cells. Navicula halo- 

 phila (Grun.) CL, Synedra ulna (Nitz.) Ehr., 5. ruvipens var. jragi- 

 larioides Grun. 



(4) The gametes behave according to no rule; the auxospore 

 position varies. Achnantbes brevipes Ag., A. lanceolata Breb., A. hn- 

 giceps Ag., Navicula didyvm (Ehr.) Kiitz., N. fonticola Grun., N. 

 hybrida Herib. & Per., Nitzschia longissima (Breb.) Ralfs., Pleuro- 

 sigina nubecula W. Sm. 



Normal Type B 



Spermatozoa and an tgg cell are formed (Figs. 5 to 12). 



( 1 ) An antheridial cell buds off two spermatozoid mother cells 

 each of which produces two spermatozoids. One oogonium produces 

 one tgg cell. A spermatozoid enters the tg^ and a zygote is formed. 

 Me I o sir a variaus Ag. 



(2) Four spermatozoa are produced from an antheridial cell. 

 One oogonium produces one egg cell. A spermatozoon enters the 

 egg and a zygote is formed. Cyclotella sp. 



Reduced Type A 



Two mother cells each build one gamete; these fuse to form a 

 single auxospore (Figs. 13 to 15). 



( 1 ) The gametes behave isogamously. Cocconeis pediculus Ehr., 

 C. placentula Ehr., C. pi ac en tula var. klinor aphis Geitler, C. placen- 



