CHAPTER II. 



THE MATURATION AND IMPREGNATION OF THE OVUM. 



Maturation of the ovum and formation of the polar bodies. 



IN the preceding chapter the changes in the ovum were described 

 nearly up to the period when it became ripe, and ready to be 

 impregnated. Preparatory to the act of impregnation there 

 take place however a series of remarkable changes, which more 

 especially concern the germinal vesicle. 



The attention of a large number of investigators has recently been 

 directed to these changes as well 

 as to the phenomena of impregna- 

 tion. The results of their investi- 

 gations will be described in the 

 present chapter ; but for an histori- 

 cal account of these investigations, 

 as well as for a determination of 

 the delicate questions of priority, 

 the reader is referred to Fol's 

 memoir (No. 87), and to a paper 

 by the author (No. 81). 



The nature of the changes 



which take place in the 

 maturation of the ovum may 

 perhaps be most convenient- 

 ly displayed by following the 

 history of a single ovum. 

 For this purpose the eggs of 

 Asterias glacialis, which have 



FlG. 22. RlPE OVUM OF ASTERIAS GLA- 

 CIALIS ENVELOPED IN A MUCILAGINOUS 

 ENVELOPE, AND CONTAINING AN ECCEN- 



GERMINAL VESICLE AND GERMINAL 



(copied from Fol). 



recently formed the subject of a series of beautiful researches 

 by Fol (87), may be selected. 



The ripe ovum (fig. 22), when detached from the ovary, is 

 formed of a granular vitellus enveloped in a mucilaginous coat, 



