Question

Why does hydra shows cross fertilization instead of self fertilization in some cases

Answer 1

Cross-fertilisation occurs as a rule in the different species of Hydra. To avoid self-fertilisation, even in monoecious species, the testes mature first, i.e., protandrous .

Answer 2

The reason why hydra shows cross fertilization instead of self fertilization in some cases  is as follows:

• In cases of different species of Hydra cross fertilization occurs. This type of fertilization helps in maintaining greater range for natural selection.
• From the testis of one Hydra,  the spermatozoa releases and swims in water with tails.
• Then it comes into contact with another Hydra's ovum.
• The ovum is penetrated by only one spermatozoon and gets fertilized.
• This forms zygote which diploid.