OF THE CELL THEORY 187 



regards vigour of offspring is well known. Minot 

 has independently suggested and strongly supported 

 the same view. A serious difficulty however has 

 been raised to this view by Weismann, who points 

 out that if the male element in the egg is got rid 

 of completely by extrusion of the polar bodies, then 

 it becomes very difficult to understand the trans- 

 mission of male ancestral characters through the 

 mother. It is well known that children may 

 inherit peculiarities of their grandfather on the 

 mother's side, and this, according to Weismann, 

 should not be possible if the extrusion of the polar 

 bodies removes all male elements from the egg. 

 We must suppose that a small remnant is or may 

 be left behind ; but then, asks Weismann, why 

 should any be eliminated at all if it is not necesary 

 that all should be got rid of ? 



The matter is very far from a simple one. 

 Weismann himself has shown that in various 

 parthenogenetic Crustacea, Polyphemus, Moina, 

 Daphnia, and others, only one polar body is 

 extruded ; and Blochmann in 1887 announced 

 that in Aphis the parthenogenetic eggs extrude one 

 polar body only, while those that require fertili- 

 sation extrude two. This seems to indicate that 

 the two polar bodies may have very different value 

 in spite of the close similarity in their modes of 

 formation ; for the extrusion of one polar body 

 seems to leave the egg still capable of developing 

 without fertilisation ; while after two polar bodies 

 are extruded, fertilisation is necessary for develop- 

 ment to occur. 



