84 MAN AND THE LOWER ANIMALS n 



mass of viscid nutritive matter the yelk within 

 which is enclosed a second much more delicate 

 spheroidal bag, called the germinal vesicle (a). 

 In this, lastly, lies a more solid rounded body, 

 termed the germinal spot (b). 



The egg, or Ovum is originally formed within 

 a gland, from which, in due season, it becomes 

 detached, and passes into the living chamber fitted 

 for its protection and maintenance during the 

 protracted process of gestation. Here, when 

 subjected to the required conditions, this minute 

 and apparently insignificant particle of living 

 matter becomes animated by a new and mysteri- 

 ous activity. The germinal vesicle and spot cease 

 to be discernible (their precise fate being one of 

 the yet unsolved problems of embryology), but 

 the yelk becomes circumferentially indented, as if 

 an invisible knife had been drawn round it, and 

 thus appears divided into two hemispheres (Fig. 

 13, C). 



By the repetition of this process in various 

 planes, these hemispheres become subdivided, so 

 that four segments are produced (D) ; and these, 

 in like manner, divide and subdivide again, until 

 the whole yelk is converted into a mass of 

 granules, each of which consists of a minute 

 spheroid of yelk-substance, inclosing a central 

 particle, the so-called nucleus (F). Nature, by 

 this process, has attained much the same result 

 as that which a human artificer arrives at by hia 



