Reproductive System – Earthworm, Cockroach, Frog

Introduction

Reproduction is the process of offspring production. There are two main types of reproduction – sexual and asexual reproduction. In sexual reproduction, a new organism is created when the genetic information from two different sexes combine. In asexual reproduction, one parent duplicates itself to form a genetically matching offspring. Animals have a distinct reproductive system. The animal reproductive system has been explained here with the examples of earthworm, cockroach and frog.

Reproductive System of Earthworm

Earthworms are bisexual or monoecious, that is, they have both male and female reproductive organs.

Male reproductive organs:

Earthworms are protandrous, which means that their testis matures before the ovary. The male reproductive system consists of the testis, testis sac, seminal vesicles, vasa deferentia, prostate glands and accessory glands.

• Testis – There are two pairs of testes. The testis is a minute, white globe-like structure located in each pair in the tenth and eleventh segments respectively. The testis is covered with the testis sac separately
• Vasa deferentia – Two pairs of vasa deferentia are present and each extends from the periductal funnels and are connected to the prostatic duct
• Accessory Glands – Two pairs of accessory glands are located in the seventeenth and nineteenth segments respectively
• Spermatheca – Earthworms have four pairs of spermatheca situated in the sixth to ninth segment, one pair in each segment respectively. They receive and store spermatozoa in the process of copulation
• Seminal vesicles – Two pairs of seminal vesicles are located in the eleventh and twelfth segments where storage and maturation occur

Female reproductive organs:

• Ovaries and Oviduct – The female reproductive system consists of the ovaries and oviduct. A pair of the small, white lobulated structure is attached at the inter-segmental septum of the twelfth and thirteenth segments
• Ovarian funnels – Ovarian funnels are present below the ovaries and connected to the oviduct, joined and opened as a single female genital pore located on the fourteenth segment

Copulation – When two earthworms come and contact each other, mating takes place juxtaposing opposite gonadal openings and there is a transfer of sperm into other earthworms

Reproductive System of Cockroach

The reproductive system of cockroaches is unisexual or dioecious.

Male reproductive organs:

The male reproductive system of cockroaches consists of the testis, phallic or conglobate gland, mushroom gland (utriculi majors and utriculi previous) vas deferens, ejaculatory duct, conglobate gland, male genital pore, genital pouch and gonapophysis or phallometric. These are located in the abdominal part of the cockroach.

• Testis – There is a pair of testis present in each dorsal lateral side of the four, five and six segments. Each testis is three-lobe and consists of about 30 to 40 small white transparent follicles arranged in the longitudinal series. The testis appears to be well-developed in the young cockroach and full of sperms. The testis becomes non-functional and decreases in the old cockroach
• Vasa deferentia – Vasa deferentia comes one from each testis and runs posteriorly downwards to open into the ejaculatory duct through the seminal vesicle
• Ejaculatory duct – The ejaculatory duct is a single, median muscular duct that extends posteriorly and opens into the genital pouch through the male genital pore which lies beneath the anus
• Mushroom gland or Utricular gland – The junction of two vasa deferentia and ejaculatory ducts are surrounded by a complex mushroom gland consisting of utriculi majors and utriculi breviores. Utriculi majors are long, slender peripheral tubules filled with sperms
• Phallic or conglobate – This is a long accessory gland. Its anterior portion lies in the sixth segment and is elongated posteriorly into a tubular structure. It opens by a separate aperture that appears near the male gonopore
• External genitalia – Asymmetrical structures surround the male gonopore at the end of the abdomen. There are three phylloxera found in the external genitalia
• Right phylloxera – It is present in the middle dorsal position. It has two membranous lobes with a saw-toothed edge and two large teeth
• Left phylloxera – It has a wide base where many portions evolve. On the left side is a long slender arm with a curvy hook-like structure called titillation. After that, there are short and wide arm ends with a hammer-like head called pseudopenis. Next to the pseudopenis are three small lobes called the aspirate lobes
• Ventral phylloxera – It lies just beneath the right phylloxera. This appears in brown and holds male gonopore
• Spermatophore – When the cockroach is young, the testis can produce sperms and move to seminal vesicles through vasa deference for storage. The sperms are joined together to form a bundle shape called a spermatophore. This spermatophore is released during the copulation of the cockroaches

Female reproductive organs:

The female reproductive system of the cockroach comprises a pair of ovaries, vagina, genital pouch and collateral glands. It also includes spermatheca and external genitalia.

• Ovaries – Two big pale-coloured ovaries can be seen in diagrams as found in the fourth, fifth,and sixth segments
• Ovarian tubules of ovarioles – Each ovary forms a bundle of eight ovarian tubules of ovarioles. An ovariole is made up of an epithelial layer and some connective tissue
• Oviduct – The stalk is raised from one end of the ovariole to the muscular wall called the oviduct
• Vagina – Both the oviducts join together to form a common tubule called the vagina
• Accessory reproductive glands – The genital pouch has been further split into genital chamber ends in the oothecal chamber where ootheca are developed. These are called the accessory reproductive glands
• Spermatheca – These spermathecae are different in their appearance. Both spermatheca are connected and end with a single duct

Copulation – Male cockroaches secrete a sugar-rich substance from a gland present in the abdomen area. These sugar glands are exposed when the male cockroaches lift their wings and turn their rear towards the female cockroaches to lure them

Reproductive System of Frog

The reproductive system of frogs is unisexual. Male frogs are bigger compared to female frogs. Also, male frogs have vocal cards, whereas female frogs do not have them.

Male reproductive organs:

It consists of the testis, vasa deferentia, seminal vesicle and urinogenital ducts.

• Testis – Male frogs have pairs of testes that are pale in colour and oval in shape. The testis is covered by the peritoneum fixed to the wall of the kidney. Each testis has coiled filaments called seminiferous tubules that are connected by connective tissue. Each tubule is covered by a membrane. The seminiferous tubules produce spermatozoa
• Vasa deferentia – A combination of 10 to 12 ducts arise from the testes and are covered by the connective tissue. A group of ducts is called rete testis
• Seminal vesicle – Seminal vesicle is the portion where sperms are stored until copulation takes place. It consists of fructose that gives nutrients to the sperms
• Urino genital ducts –  This is also called the ureter. Here, sperm is passed out along with urine
• Sperm formation –  The formation of the stem is known as spermatogenesis. It consist of four phase-

Multiplication phase, Growth phase, Maturation phase, and Metamorphosis

Female reproductive organs:

It consists of a pair of ovaries, oviduct, oviduct funnel, middle region and uterus.

• Ovary – A pair of dark-coloured organs are surrounded by a membrane called mesovarium. The ovary is filled with eggs. Ova is also called an egg. During ovulation, ova come out of the abdomen
• Oviduct – The oviduct is a slender and elongated duct that connects to the kidneys
• Oviduct funnel – From the oviduct, a wide opening is situated near the lungs. This broad opening is also called ostium
• Uterus –  It is the thin-walled structure that appears near the cloaca. After ovulation, the egg passes from the ovary with a fluid called the coelomic fluid. The ova are covered by a protein called albumin and reach into the uterus
• Egg formation – The maturation of the egg requires a few steps: the multiplication phase, the growth phase and the maturation phase

Copulation – Male frogs wrap their hands around the female frogs during the mating process. The female frogs deposit the eggs and the male frogs fertilise the eggs, which further hatch into tadpoles and later develop into froglets

Conclusion

Earthworms are bisexual in nature. The male reproductive system of earthworms consists of testes, vasa deferentia, accessory glands, spermatheca  and seminal vesicles. The female reproductive system consists of ovaries and oviducts. Cockroaches are unisexual animals by nature. The male and female reproductive systems of cockroaches are well-developed. The sexes are different for frogs and well-developed organs are present in both male and female frogs. During breeding, the male and female frogs enter into a temporary reunion process.