118 THE BIOLOGY OF THE ANIMAL 



in this manner the ovum becomes fitted for 

 the reception of the sperm-cell (fertilization). 

 How do the polar globules compare in size 

 with the ovum ? Do you ever find that more 

 or fewer than two are formed? How long 

 does it take the first one to form? The 

 second? Does the second form in the same 

 place as the first? Always? Can you suggest 

 any reasons why the polar globules are formed ? 

 Draw the different stages of formation of the polar 

 bodies. 



c. Fertilization. 



1. The union of the sexual cells. — Mix together on 

 the slide a drop of water containing a few eggs 

 and one containing spermatozoa, put on the 

 cover-glass supported by bits of wax, and 

 examine under the high power. How do the 

 spermatozoa behave? How the ova? Ifote 

 that the most of the sperm-cells collect around 

 the eggs. Can you see the entrance of the 

 sperm-cell into the agg ? Does it take place at 

 any particular point ? How many sperm-cells 

 enter the same egg ? Notice that a short time 

 after the sperm and ova are mixed a clear area 

 appears between the wall and the contents of 

 certain ova. These ova have been fertilized, 

 although the entrance of the spermatozoon 

 may have escaped observation. 



d. The consequences of fertilization. 



1. The first division or segmentation of the ovum. — 

 A few minutes after the sperm and eggs have 

 been mixed some of the latter will show a 

 notch beginning to form at one margin of the 



