Reproductive System in Earthworms, Practice Problems and FAQs

Food wastes management is a great issue in many homes. But if you have a backyard in the home with some plants, you can use the waste food as a manure for the plants. But how is this food converted into manure? The process of the conversion of organic matter into manure or fertiliser is called composting. There are some organisms that live in the soil which help in the process of composting like the mites, centipedes, ants, earthworms etc. These animals grind, tear and chew the materials into smaller pieces. Then the microbial decomposition happens.

So among all these organisms, there is one organism that pops up every time we dig the soil. Which is it? Yes, the earthworm, the friend of farmers!! Why are they called so? It is because of the same reason for increasing soil fertility, through recycling organic wastes. They also help to loosen the soil through making their way to find food and mates.

                                      GIF: Earthworm

Within a single dig we can find a lot of earthworms. Right? Especially during the rainy season, their number will be more. What is the reason for this? The reason is that the reproduction of earthworms happens more in the rainy season. So how do they reproduce? They should have proper reproductive structures for it. Are these structures present in the same organism or different? Let’s find it out through discussing the reproductive system of an earthworm.

Table of contents

• Reproduction in earthworm
• Male reproductive system of earthworm
• Female reproductive system of earthworm
• Fertilisation and development in earthworm
• Practice Problems
• FAQs

Reproduction in earthworm

The body of earthworms are cylindrical and metamerically segmented. They have almost 100 to 120 segments in their body.

                           Fig: Segments in earthworm

Hermaphrodite

They are bisexual, monecious or hermaphroditic organisms, which means both female and male organs of reproduction are present within the same organism. Hence an earthworm has both testes and ovaries. Earthworms are also protandrous, which means the testis matures earlier compared to the ovary. Their male and female genital apertures are different and are present on the ventral side of the body. The female pores are in the pre-clitellar segment and the male pores are in the clitellar segment.

                                          Fig: Genital pores of earthworm

Cross fertilisation

These organisms can not fertilise their own eggs. Only cross fertilisation is possible in earthworms, that means they only fertilise eggs from other worms. Hence they undergoes copulation and sexual reproduction.

                              Fig: Copulation in earthworm

Male reproductive system of earthworm

The male reproductive system of an earthworm starts from the 10^th segment and ends in the 20^th segment. The major parts of a male reproductive system are as follows:

• Testes
• Testis sac
• Seminal vesicles
• Spermatic funnel
• Vasa deferentia
• Accessory glands
• Prostate glands
• Common prostatic and spermatic duct

                      Fig: Male reproductive system of earthworm

Testes

There are 2 pairs of testes in the 10^th and 11^th segments of the earthworms. They are minute and small lobed. Spermatogonia are formed in the testis. Testis possess four to eight lobules (finger-like) which possess rounded cells in groups called spermatogonia. Testes are present in the testis sac. Mature sperms from seminal vesicles move back to the testis sac and pass through the spermiducal funnel into vasa deferentia.

                                                     Fig: Testes

Testis sac

These are fluid filled, thin walled sacs linked with seminal vesicles. The spermatogonia are transferred into the testis sacs first from where they enter into the seminal vesicles.

Seminal vesicles

These are whitish large spherical structures found in 2 pairs. Each of this pair of seminal vesicles are located in the 11^th and 12^th segment. The testis sacs are open into the seminal vesicles by narrow ducts. Seminal vesicles receive the spermatogonia from the testis sacs and they help in the nourishment of the sperm. Here the spermatogonia matures to form spermatozoa in the seminal vesicles.

                                                 Fig: Seminal vesicles

Spermatic funnel

These are also called spermiducal funnels. These are normally present in 2 pairs. They are located below each testis which are present in the segment 10^th and 11^th. These funnels are also present within the testis sac. Their main function is to transport sperm. Once matured, the sperms from the seminal vesicles enter the testes sac and then pass into vasa differentia through the spermatic funnel.

                                            Fig: Spermatic funnel

Vasa deferentia

The duct that collects sperms from the spermatic funnel and transfers to the prostate gland is called vasa deferentia. These are long, narrow and tubular structures. These are found in pairs of two. Each pair is present on either side of the gastrointestinal tract. It extends from the 12^th to 18^th segment and meets the prostatic duct in the 18^th segment and forms a common prostatic and spermatic duct.

Accessory glands

Two pairs of accessory glands present in the male reproductive system of an earthworm. They can be seen as one pair each in the 17^th and 19^th segments. The secretion of these glands hold two worms during copulation. They help in pseudocopulation.

                                  Fig: Accessory glands

Prostate gland

One pair of prostate glands present in earthworms. It extends from 16^th to 20^th segments or from 17^th to 21^st segments. It produces prostatic fluid that is alkaline in nature. The prostatic fluid activates sperms and keeps them motile.

                                   Fig: Prostate gland

Common prostatic and spermatic duct

A short and thick curved prostatic duct emerges from each of the prostate glands in the 18^th segment. Prostatic duct from the prostate glands joins with the two vasa deferentia from the same side and unite to form a common duct called common prostatic and spermatic duct. Prostatic duct opens through the male genital aperture present on the ventral side of the 18^th segment.

                   Fig: Common prostatic and spermatic duct

Female reproductive system of earthworm

The female reproductive system of earthworm extends from the 6^th segment to the 9^th segment. The major parts of the female reproductive system of an earthworm are as follows:

• Spermatheca
• Ovary
• Ovarian funnel and oviduct

               Fig: Female reproductive system of earthworm

Spermatheca

Four pairs of spermatheca are present in the earthworm and it extends from 6^th to 9^th segments. The major function of spermatheca is to receive and store spermatozoa during copulation.

Ovary

One pair of ovaries present at the intersegmental septa of 12^th and 13^th segments. They produce ova.

Ovarian funnel and oviduct

Ovarian funnels are present at the base of each ovary and it leads into the oviduct. Ovarian funnel fuses with oviduct and opens on the ventral side as a single median female genital pore on the 14th segment.

Fertilisation and development in earthworm

Copulation of earthworms usually takes place during the rainy season. The sexual mode of fertilisation in earthworm is a cross fertilisation. Hence a mutual exchange of sperm or spermatozoa occurs between two worms during mating through juxtaposing.

                         Fig: Copulation in earthworms

Cocoons

The mature sperms, eggs and nutritive fluid after exchange are encased in the cocoons. Cocoons are deposited in the soil and the fertilisation of sperm and ova occurs inside the cocoons. The embryo formed by the fertilisation is held by the cocoon until hatching.

                             Fig: Earthworm cocoons

Direct development

20 to 25 worms are formed in each cocoon. It will take 3 weeks for the development of earthworms inside the cocoon. There is no larval stage in the development of earthworm and it is called a direct development.

                       GIF: Young earthworms

Practice Problems

1. In which segment of the earthworm, the female pores are present?

1. Pre-clitellar
2. Clitellar
3. Post clitellar
4. Both pre-clitellar and clitellar

Solution: Earthworms are bisexual, monecious or hermaphroditic organisms, which means both female and male organs of reproduction are present within the same organism. Hence an earthworm has both testes and ovaries. Earthworms are also protandrous, which means the testis matures earlier compared to the ovary. Their male and female genital apertures are different and are present on the ventral side of the body. The female pores are in the pre-clitellar segment and the male pores are in the clitellar segment. Hence the correct option is a.

Fig: Female genital pores of earthworm

2. Which of the following male reproductive structures of an earthworm is seen in 10^th and 11^th segments?

1. Testes
2. Vasa deferentia
3. Accessory gland
4. Prostate gland

Solution: There are 2 pairs of testes in the 10^th and 11^th segments of the earthworm. They are minute and small lobed. Sperms are formed in the testis. Mature sperms from seminal vesicles move back to the testis sac and pass through the spermidical funnel into vasa deferentia. Hence the correct option is a.

Fig: Testes

3. Assertion: The development of earthworms is direct.

Reason: There is no larval stage in the development of earthworm

Find out the correct option for the above assertion and reason from the following.

1. Both the assertion and the reason are true and reason is the correct explanation of the assertion
2. Both the assertion and the reason are true, but the reason is not the correct explanation of the assertion
3. Assertion is true, but the reason is false
4. Both assertion and reason are false

Solution: The mature sperms, eggs and nutritive fluid after exchange are encased in the cocoons. Cocoons are deposited in the soil and the fertilisation of sperm and ova occurs inside the cocoons. The embryo formed by the fertilisation is held by the cocoon until hatching. 20 to 25 worms are formed in each cocoon. It will take 3 weeks for the development of earthworms inside the cocoon. There is no larval stage in the development of earthworm and it is called a direct development. Hence the correct option is a.

4. Which duct opens out through the male genital pore?

1. Prostatic duct
2. Vasa deferentia
3. Common prostatic and spermatic duct
4. Oviduct

Solution: A short, thick curved prostatic duct emerges from each of the prostate glands in the 18^th segment. The prostatic duct from the prostate gland joins with the two vasa deferentia present on the same side and unite to form a common duct called common prostatic and spermatic duct. Prostatic duct opens separately through a male genital aperture on the ventral side of the 18^th segment. Hence the correct option is c.

                 Fig: Common prostatic and spermatic duct

FAQs

1. Do earthworms have sense organs?
Answer: Earthworms have no eyes, but they do have light receptors which can sensitise when they are in the dark, or in the light. They can sense the vibrations transmitted through the soil. The first segment of earthworm is known as the peristomium. It contains mouth and prostomium. Prostomium is a fleshy lobe overhanging the mouth which is sensory in function. Earthworms also possess specialised chemoreceptors on the anterior region which react to chemical stimuli.

                             Fig: Peristomium

2. How do earthworms respire?
Answer: Earthworms lack specialised breathing devices. Respiratory exchange occurs through the moist body surface into their bloodstream. Oxygen dissolves into the mucous coating of the skin. Dissolved oxygen passes through the skin and the capillaries lining the skin.

3. Which is the longest earthworm?
Answer: The longest known earthworm in the world, stretching to more than 2m, is the Australian Giant Gippsland earthworm Megascolides australis.

        Fig: Megascolides australis

4. Which are the two earthworms that are commonly found in India?
Answer: In India there are two common types of earthworms as follows:

• Lumbricus
• Pheretima

                                       Fig: Common Indian earthworms