WHY LIKE BEGETS LIKE 13 



proportion to the size of the whole egg. In Fig. I is 

 shown the structure of a typical small ovum, showing 

 the germinal vesicle, and a large number of granular 

 masses of yolk. Eggs are usually jM-oduced in relatively 

 small numbers, yet certain animals, such as a number 

 of the fishes, produce enormous numbers. 



The sperms, having been brought into the neighbour- 

 hood of the egg, are, in some way which is not under- 

 stood, attracted to it. They cluster round the outside 

 of the ovum, and one of them pushes itself into the 

 substance of the egg. One sperm only enters the egg, 



Fio. 1. — The Ovum and the Sperm, g.v. The germinal vesicle 



or nucleus. 



for immediately on the entry of the first, the outermost 

 layer becomes so altered that the others cannot pene- 

 trate it. The head of the sperm, leaving its tail behind, 

 gradually travels toward the germinal vesicle, and the 

 two bodies fuse into one. This process is known as 

 fertihsation, and the result is the fertilised egg. 



The fertiUsed egg is endowed with a remarkable 

 energy. It begins to absorb nourishment, either the 

 yolk contained %Wthin itself or food obtained from the 

 female parent. The original single cell divides and re- 

 divides rapidly, until a hollow ball of cells is formed. 

 Then one-half of the ball is, as it were, pushed inside 

 the other, so that a body like a double-walled cup 



