182 SOME RECENT DEVELOPMENTS 



frog, the first polar body may be extruded prior to 

 fertilisation, and the second after or during the 

 process ; while in some cases, as in Ascaris, 

 according to van Beneden, both polar bodies are 

 extruded after the entrance of the spermatozoon. 

 In 1875 Btitschli showed that in Nematodes the 

 extrusion of polar bodies is accompanied by the 

 formation of a nuclear spindle, and by other 

 changes similar to those seen in indirect nuclear 

 division. He in consequence suggested the view 

 that the formation of a polar body is really a 

 division of the egg cell into two very unequal 

 portions, and is accompanied by the ordinary 

 nuclear changes seen in typical cases of mitosis. 

 This view has since been widely adopted, though 

 authorities are not yet agreed as to whether any 

 part of the protoplasm of the egg is extruded with 

 the daughter nucleus in the polar body. The point 

 is of considerable interest, for on one view the 

 whole process would be one of cell division, on 

 the other merely nuclear division with extrusion 

 of one of the daughter nuclei. The balance of 

 opinion inclines strongly towards the former of 

 these views, but the point cannot be considered 

 definitely settled as yet. 



The changes that occur in the egg nucleus 

 during the formation of polar bodies have been 

 recently studied with great care by many observers. 

 In the frog's egg Oscar Schultze has shown that 

 at the time of ripening of the egg the nucleus 

 undergoes important changes. Previous to this 

 time it has been of very large size, as much as a 



