7 FECUNDATION ; NON-MOTILE ISOGAMETES. 



nuclei can be distinguished (Fig. 26, D). According to Raciborski 

 ('96) the fusion may be delayed until the germination of the zygote. 

 The full significance of the formation of the beaks into which the 

 nuclei wander, the division of the latter, and the cutting off of the 

 small cells which degenerate, can be more fully understood only after 

 the process of sexual repi'oduction is known in other and related forms. 

 The two small cells cut off in the ends of the beaks may, however, be 



FIG. 26. Fusion of sexual nuclei in Basidiobolus ranarum. (After Fairchild.) 

 C, the sexual nuclei are in contact. D, zygote with fusion nucleus and thick cell- wall. 



reasonably regarded as degenerate gametes, although it may seem idle 

 to attempt to explain or to bring into line the various peculiar phenom- 

 ena brought out in the several preceding paragraphs that pertain to 

 the desmids, diatoms, Basidiobolus and Spirogyra. In the desmids, 

 diatoms and Basidiobolus, it is possible that all these phenomena 

 may have resulted independently from similar causes acting during a 

 large part of the phylogenetic history of the respective groups of plants. 



