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 



• Professor Alfred Newton, article on "Embryology." 



