ai4 FATHERLESS FROGS 



rape-seed, which is imbedded in a thin jelly, and is familiar 

 to those who are drawn by curiosity to look into the waters 

 of wayside ponds in spring) is a single cell or corpuscle of 

 protoplasm distended with dark-coloured and other granules 

 of nutrient substance. A single sperm (though, requiring 

 the microscope to render it visible) is also a single cell. 

 It is a minute oval body, with a long serpentine tail of 

 actively undulating protoplasm. Hundreds of thousands 

 of these are shed into the water at the breeding season by 

 the male frog. One is enough to fertilise the egg. The 

 sperm-cells swim in the water, and are chemically attracted 

 by the eggs. As there are so many sperms, one of them is 

 sure to reach each black egg-sphere. It drives its way into 

 the substance of the egg, making a minute hole in its 

 surface ; then the protoplasm of the sperm fuses with the 

 protoplasm of the egg, and becomes intimately mixed with 

 it. The egg-cell has a " nucleus," that dense, peculiar, 

 deep-lying, and well-marked " kernel " of its protoplasm 

 which all cells have. It is of essential importance in the 

 life and activity of the cell. The sperm-cell has also a 

 " nucleus," and now (as has been carefully asertained) the 

 nucleus of the sperm and the nucleus of the egg-cell unite 

 and form one single nucleus. The egg is thereupon said 

 to be " fertilised " — that is to say, " rendered fertile," It 

 at once commences to move. Its surface ripples and 

 contracts and nips in deeply, so that the sphere is marked 

 out into two hemispheres. These are two "cells," or 

 masses of protoplasm, adhering to each other. Each is 

 provided with its own distinct nucleus or cell-kernel, for 

 the first step in the division of the egg-sphere is the 

 division within it of its newly constituted nucleus into two, 

 each half consisting of nearly equal proportions of the 

 mingled substance of the sperm-nucleus and the egg- 

 nucleus. The two first cells or hemispheres again divide, 

 and so the process goes on until the little black egg has 



