NATURAL HISTORY NOTES 51 



the everyday vocabulary of all sciences, and 



perhaps more than most of embryology 



few unlearned minds would contemplate 

 the breakfast egg with their wonted calm 

 were they suddenly made aware of the fact 

 that it was full of blastoderm and hypo- 

 blast— make it unwise to follow the 

 process of incubation in the egg with any 

 approach to scientific accuracy, yet a hint 

 of the unseen changes so little known to 

 those who may be handling and setting 

 thousands of eggs every season, has— if 

 no particular practical value— at least a 

 certain interest to any one who likes to 

 know the ' why and wherefore ' of things. 

 At the time of fertilization the egg or 

 ovum consists of a skin-covered globe of 

 yellow yolk, traversed by a small funnel 

 of white yolk on the top of which rests 

 the germ of life. This germinal disk— as 

 it is known from its shape— at once begins 

 to break up into a number of cells, which 

 step by step build up the complex mechan- 

 ism of the embryo.^ In the twenty hours 



1 Professor Alfred Newton, article on "Embryology." 



