Most hydra are dioecious, but some hydra are monoecious. Self-indulgence is a sexual process. The union of sperm and ovum of the same animal is called insemination. Even though hydra is bisexual, self-fertilization does not occur. In the same hydra, spermatozoa and ova are produced in two different seasons. In hydra the eggs are immature at the time when the sperm are mature. Again, when the egg is mature the sperm is immature. Therefore sperm and egg of the same hydra can never meet. This is why self-fertilization does not occur in hydra. In hydra, only purification occurs. Dr. Siddiq Publications