STAEFISH 117 



2. The ovTim. — Collect some ova in the manner de- 

 scribed for spermatozoa. Put them under the 

 low power and note their shape, size, color, etc. 

 Is an ovum large enough to be seen without 

 the microscope ? Put on the high power and 

 study their structure. Can you, with or with- 

 out reagents, make out a cell- wall, protoplasm, 

 and nucleus ? Does the egg sink to the bottom 

 or does it float? Compare ovum and sperma- 

 tozoon as regards shape, size, color, structure, 

 motions etc. "What reasons can you suggest 

 for the differences ? 

 Draw an unf ertOized, i. e., ovarian, ovum. 



b. Preparation of the ovum for fertilization. 



1. The formation of the polar globules or "direc- 

 tion-cells." — Examine a number of unfertil- 

 ized living ova to see if some cannot be found 

 which are pushing out a small protuberance at 

 one margin of the yolk {2}rotoj>lasm), just under 

 the membrane or cell-wall. This prominence in- 

 creases in size, and finally becomes divided off 

 from the surface of the yolk as the " first polar 

 globule." Soon afterwards a second is formed 

 in the same manner, and the two come to lie 

 side by side under the egg-membrane. Each 

 globule contains a portion of the nucleus of the 

 ovum. Stain some of the ova with carmine or 

 hgematoxylin to prove this last statement. The 

 process of the formation of the polar globules 

 is known as the " maturation of the ovum " ;* 



* A process somewhat similar to this has been seen to take place 

 in the spermatozoa of certain animals. 



