A complex dialogue exists between ovum and sperm. The egg activates the sperm metabolism that is essential for fertilization, and the sperm reciprocates by activating the egg metabolism needed for the onset of development.
Egg: The ovum is often called an egg. The eggs appear as mustard-grain and can be seen in naked eyes. The shape of the ovum of toad is rounded, one end is blackish and the other end is whitish in colour. At the blackish end of ovum remains the cytoplasm and nucleus and in the whitish end portion remains the yolk. The amount of yolk in the ovum of the toad is plenty. Each ovum remains covered by a thin membrane. The egg has the yolk side is called a “Telolecithal’ egg.
Sperm: The sperm of toad cannot be seen with naked eyes. The spenn cell is divided into three parts, such as Head part, middle part or neck, Tail part
(i) Head: The head of the sperm is oval shaped Inside it lies the nucleus. Where remains the haploid number of chromosomes.
(ii) Neck or Middle part: The middle small portion between the head and tail of sperm is the neck. In this part of the cell remain centrosome and mitochondria.
(iii) Tail: The narrow, elongated and motile part of the sperm is called the tail. With the help of this narrow tail, the sperm swims in water.