ON SAPROLEGN3J5. 291 



observed to be thrown off by animal ova prior to fertilisation,^ 

 may not the hypothesis thrown out by Balfour apply also to the 

 cases observed by De Bary ? 



De Bary shows that these protoplasmic bodies are taken 

 up again, and that such oospheres as have again absorbed 

 the thrown-off bodies, become ripe oospores, capable of ger- 

 mination after a period of rest without being fertilised. Bal- 

 four suggested that the " polar cells " are thrown off to prevent 

 parthenogenesis, i.e. to prevent the egg dividing up and 

 developing an embryo which has not benefited (in Darwin's 

 sense) by receiving protoplasm from a distance ; the further 

 development of the non-fertilised oospores (ova) of Sapro- 

 legnise may be possible because the *' polar cells" are again 

 absorbed? Here, however, the proper limits of the present 

 essay have been passed. 



' C f. Balfour's ' Comparative Embryology,' p. 58. 



