192 THE BEGINNINGS OF LIFE. 



survives and may even increase in size after the for- 

 mation of the germinal vesicles. According to Braun, 

 c The nucleus of the embyro-sac is only dissolved during 

 or shortly before the period of fertilization, and then 

 a profound reconstruction commences in the interior 

 of the embyro-sac, expressed in the production of 

 daughter cells likewise free, but so numerous that they 

 soon exhaust the independent life of the former, and 

 the entire cavity becomes filled up by the cohering 

 newly-formed cells. The tissue produced in this way 

 is the endosperm, or, as it is called, the albumen of 

 the seed, in which the developing embryo of the new 

 plant then becomes imbedded. The endosperm cells, 

 like the germinal vesicles, originate as free nuclei in 

 the fluid of the embryo-sac, which subsequently becomes 

 surrounded by masses of contents and clothed with 

 membranes. The cells thus formed very soon combine 

 into a continuous parenchyma, in which there is no 

 longer evidence of the origin from free cells.' Such is 

 the mode of origin and development of the seeds of 

 most of the flowering plants. 



If we now turn our attention to some of the methods 

 by which reproductive germs, or ova, are produced in 

 the members of the Protistic and Animal Kingdoms, 

 we shall find these strikingly analogous to the modes of 

 origin of reproductive units, such as we have just been 

 citing, amongst the various members of the Vegetable 

 Kingdom. 



The first example to which we shall refer will be the 



