VI.] THEIR SIGNIFICANCE IN HEREDITY. 355 



from them, will make my hypothesis upon the histogenetic 

 nucleoplasm of the germ-cells appear m a more favourable 

 light to the authorities above-named. 



My hypothesis has at all events the one merit that it has led 

 me to fruitful investigations. 



If the formation of polar bodies really means the removal 

 of ovogenetic nucleoplasm from the mature egg, they must also 

 be found in parthenogenetic eggs; inasmuch as the latter 

 possess a specific histological structure equal to that found 

 in eggs requiring fertilization. If, therefore, it were possible 

 to observe the formation of polar bodies in eggs which de- 

 velope parthenogenetically, such an observation would not 

 form a proof of the validity of my interpretation ; but it 

 would be a fact which harmonized with it, and negatived a 

 suggestion which, if confirmed, would have been fatal to the 

 hypothesis. Minot, Balfour, and van Beneden, from the point 

 of view afforded by their theories, were compelled to suppose 

 that polar bodies are wanting in parthenogenetic eggs ; and the 

 facts which were known at that time favoured such an opinion, 

 for in spite of many attempts, no one had ever succeeded in 

 proving the formation of these bodies by parthenogenetic eggs. 



During the summer of 1885 I first succeeded in ascertaining 

 that a single polar body is expelled from the parthenogenetic 

 summer-egg of one of the Daphnidae, — Polyp/ienius ocu/us\ 

 Thus my interpretation of the process in question received 

 support, while it seemed to me that Minot's interpretation of 

 polar bodies had been refuted ; for if these bodies are formed 

 in the parthenogenetic eggs of a single species, just as in eggs 

 which require fertilization, it follows that the expulsion of polar 

 bodies cannot signify the removal of the male element from 

 the egg. 



The desire to throw light upon the significance of polar 

 bodies has been the only cause of my investigation. At the 

 same time I hoped by this means to gain further knowledge as 

 to the nature of parthenogenesis. 



In the third part of the essay on ' The Continuity of the 

 Germ-plasm' (see p. 229) I attempted to make clear the nature 

 of parthenogenesis, and I arrived at the conclusion that the 



' This observation was first published as a note at the end of the 

 fourth Essay in the present volume. See p. 255. 



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