Question

Earthworms are bisexual but still cross-fertilization is common in them. This is because

• A. spermatozoa of different earthworms are different
• B. spermatozoa and ova mature at different times in the same earthworm
• C. ova from other earthworms may be larger
• D. ova mature earlier than spermatozoa

Answer 1

The correct option is B spermatozoa and ova mature at different times in the same earthworm

Earthworms are bisexual in nature. They have both male and female sex organs in the same organism (hermaphrodites). Even though they are monoecious, self fertilisation does not occur in these organisms. This is because the male gonads mature earlier than female gonads and hence spermatozoa are produced earlier than ova (eggs). This is called protandry.
Hence, self-fertilisation is prevented due to protandry.