SEXUAL RI'PRODUCTION IN DIATOMS 89 



giimcte to mature is the one that starts the movement. Carefully con- 

 trolled experiments are necessary to determine the true condition. 



FUSION OF GAMETES 



The fusion of gametes in diatoms is of three types. Isogamous 

 fusion is the result of equal movement of the gametes or of copula- 

 tion of the gametes with both of them in situ. Anisogamous fusion is 

 the result of unequal movement of the gametes. Autogamous fusion 

 is the result of the fusion of two gametes in the same mother cell. 



Isogamous fusion may be of three types. In one type, as in 

 Amphora and Denticula (Geitler, 1932), the two gametes from each 



Figures 1 to 12 and 16 to 29 are taken from various papers by Lothar Geitler. 



Figures 13 to 15 and 20 to 22 after Fritsch. 



Fig. 1. Goniphone7na panmlmu var. viicropus (Kiitz.) CI., two mother cells in 

 copulation jelly with two gametes in each cell (x 750, approx.). 



Fig. 2, and 3. Go?>rpho?ie?Na parz'-iilmn var. viicropus (Kiitz.) CI., showing the 

 fusion of gametes (x 750, approx.). 



Fig. 4. Go7nphone?>ia parviilmn var. micro pus (Kiitz.) CI., one zygote in each 

 mother cell (x 750, approx.). 



Fig. 5. Spermatogenesis in Cyclotella sp., beginning of first meiotic division (x 

 900, approx.). 



Fig. 6. Cyclotella sp., telophase of first meiotic division (x 900, approx.). 



Fig. 7. Cyclotella sp., telophase of second meiotic division (x 900, approx.). 



Fig. 8. Cyclotella sp., daughter protoplasts (x 900, approx.). 



Fig. 9. Cyclotella sp., spermatozoa (x 900, approx.). 



Fig. 10. Cyclotella sp., formation of oogonium (x 900, approx.). 



Fig. 11. Cyclotella sp., mature egg cell with sperm nucleus (x 900, approx.). 



Fig. 12. Cyclotella sp., zygote after fusion of sperm and egg nuclei (x900, 

 approx.). 



Fig. 13. Cocconeis place nttila var. klinor aphis Geitler, gamete formation (x 500, 

 approx.). 



Fig. 14. Cocconeis placentula var. klinorapbis Geitler, fusion of gametes ( X 500, 

 approx.). 



Fig. 15. Cocconeis placefitula var. klinorapbis Geitler, auxospore formation (X 

 500, approx.). 



Figs. 16 and 17. Govipbonenia constrictuni var. capitatuvi (Ehr.) V. H., two 

 gametes in each cell (x 400, approx.). 



Fig. 18. Goinpbone'ina constrictuni var. capitatuvi (Ehr.) V. H., zygote resulting 

 from automixis, nuclei not fused (x 400, approx.). 



Fig. 19. Govipbonema constrictum var. capitatuvi (Ehr.) V. H., zygote with 

 nucleus fused (x 400, approx.). 



Figs. 20 and 21. Cocconeis placentula var. lineata (Ehr.) CI., nuclear reorganiza- 

 tion in two approximate cells ( X 500, approx.). 



Fig. 22. Cocconeis placentula var. lineata (Ehr.) CI., auxospore resulting from 

 automixis (x 500, approx.). 



