REPRODUCTION IN INVERTEBRATES

REPRODUCTION IN INVERTEBRATES

CONTENT

1. Meaning of Reproduction
2. Reproduction in Cockroach
3. Reproduction in Housefly
4. Reproduction in Snail

Meaning of Reproduction

Reproduction is one of the activities that differentiate living organism from Non-living organisms. It is a process through which living organism replicate themselves to ensure continuity of life. Living organisms that fail to reproduce will come to extinct when all living member die.

Thus cockroaches, houseflies, snails and all invertebrates give rise to young ones after their kind. There are two types of reproduction-Asexual and sexual reproduction.

Reproduction in Cockroach

Reproduction in cockroach is sexual. The process occurs as follows:

1. Male and female mate. Sperm cells from the male are stored in a pouch on the 7^th abdominal segment of the female cockroach. This pouch is called Spermatheca.
2. Fertilisation occurs in pouch.
3. Spermatheca (Sperm pouch) forms the egg case called Ootheca. Ootheca contains between 10-16 eggs.
4. Ootheca is carried about by the female between its two hind legs for a number of days.
5. Female eventually deposit Ootheca containing the fertilised eggs in a suitable place like dark cornear of a cupboard for incubation.

Incubation period is about 30 days. At the end of incubation, the eggs hatch to give small ones that are similar to the adult except for the absence of wings, small size and pale colour. This small cockroach is called Nymph. Nymph moults a number of times to get to a full grown cockroach.

EVALUATION

1. Describe sexual reproduction in cockroach.
2. Make a diagrammatic reproduction of the process.
3. Itemise the differences between adult cockroach and a Nymph.

Reproduction in Housefly

Housefly reproduces sexually, fertilisation is internal and it undergoes Complete Metamorphosis. Mating occurs between adult male and female houseflies. Sperms mature before the eggs thus sperms are stored in sperm sacs until eggs are matured for fertilisation.

Life Cycle of a Housefly

Stages of Development in Housefly

1. Egg stage: After mating and fertilization, eggs are laid in batches of about 100 – 150 eggs.

1. Larva stage: Under favourable conditions, eggs hatch after about 24 hours into larva. Another name for larva is maggot. Maggots are cylindrical in shape; they are layer towards the anterior region and have 12 segments. At this stage, the maggot (Larva) has two spiracles, one on the 2^nd segment and the other on the 12^th segment for respiring. It has a mouth on the first segment which has a hook. Larvae grow very fast and start moulting two days after hatching from the egg. Ventral pads for movement are located on the 8^th, 9^th, 10^th segments of the larva. The larva moults twice before metamorphosing into a pupa.

3. Pupa: By covering itself with a case known as pupa case after 3 moulting the larva changes into a Pupa. Pupa is barrel-shaped and inactive. The cylindrical shape of the larva shortens and burrows into the soil. The skin hardens up and twin dark brown. Within 3-5 days under favourable conditions, the pupa hatches to give a young housefly. Cold weather however could delay hatching.

4. Imago or young adult: Fully formed adult emerges from the pupa is the pupa case breaks open out of decaying matter. The imago step for a few houses on a spot for its wings to dry up, harden and expand and flies off in search of food.

Housefly Laying Eggs

Reproduction in Snails

Terrestrials snails are hermaphrodites, a few aquatic species have separate sexes. However, self-fertilization does not occur. Mating occurs and fertilization is internal.

To replace, two matured snails pair up to inseminate each other. Each member produces a special structure called spermatophore. The spermatophore is pushed into the partner’s body thereby transferring sperm cells into the sperm pouch of each other each partner’s egg ate then fertilised with the sperm cells from the copulating partner when each is ready to lay eggs. Eggs are laid in shallow top soil while the weather is warm and damp. After about 2-4 weeks, the eggs hatch and the young ones emerge. Snails are prolific breeders. They can lay up to 100 eggs in a single breed and can lay eggs once every mouth.

Mating in Snail

Reproductive Structure of a Snail

EVALUATION

1. Briefly describe how snails reproduce.
2. What is a spermatophore?
3. What is the duration between fertilisation of eggs and eggs hatching into small snails?
4. Snails are prolific breeders. Explain