Pila reproduction.pptx

Reproduction

1. Pila reproductive system

2. Pila is dioecious and shows sexual dimorphism. Male has a smaller shell, a less swollen body whorl and a more developed penis than the female. Male reproductive system 1. Testies :
It is single and lies close to digestive gland, appears quite distinct on account of its creamy colour .
It is separated from the shell by a thin cutaneous membrane. Two types of sperms are produced in the testis eupyrene , and oligopyrene . Eupyrene sperms are small, thread-like, about 25.0 µ long and 1.2 µ broad, and with distinct head, middle piece and tail with a cilium. They are motile and can fertilize ova. Oligopyrene sperms are large, spindle shaped, about 32.5 µ long 3 µ broad with distinct head, middle piece and tail of 4 or 5 cilia. They are non-motile, incapable of fertilization and probably have some other function.

3. 2. Vasa efferentia : Several fine ducts, the vasa efferentia , arise from the different regions of the testis and unite to form large common ducts the vas deferentia .
3. Vas deferens: It is differentiated into three distinct regions
( i ) one proximal tubular part
(ii) vesicula seminalis and
(iii) Terminal glandular part.
Proximal parts of vas deferens are narrow and thin walled. It runs along the inner border of digestive gland upto the posterior renal chamber and then it runs to the left.
After reaching the pericardium it opens into the ventral side of vesicula seminalis . Vesicula seminalis is a somewhat curved, swollen and flask shaped structure with a blind rounded posterior prolongation.
It serves as a storehouse for the sperms. Its narrow tubular end leads into the glandular part. This part runs forward into the left side of the rectum.
It finally opens outside by the male genital aperture, at the tip of which genital papilla, which is a miniature second penis is situated.

4. 4. Penis :
It is a copulatory organ situated in front of the anus and remains enclosed in a thick glandualr flap, the penis sheath when not in use is a long stout and slightly curved flagellated structure with a swollen base and a tapering free end. It is highly extensile; being about 1.5 cm long but can attains a length of 4 cm during copulation. 5. Hypobranchial gland: At the base of the penis sheath is an oval, glandular thickening with pleated surface, the hypobranchial gland.
It consists of tall cells containing small basal nuclei. Due to absence of duct its secretions are released directly upon its surface

5. Female reproductive system Ovary :
It occupies the same position as the testis in male but is less extensive. In mature females it is branched and dark coloured .
Branches of the ovary or acini are single layered and flask shaped structure. Their outer rounded end is closed and the inner slender tubular end unites to form a single oviduct. Oviduct :
It is narrow and transparent tube like structure. It arises from the middle of the ovary and runs along the inner margin of the digestive gland. Near the renal organ it turns downwards and then upwards to open into the receptaculum seminis .

6. Receptaculum seminis : It is small bean shaped and lies enclosed within the cavity of posterior renal chamber. It is attached closely to thin walled pouch, arises from the wall of uterus and is called pouch of receptaculum . It is meant for storing the sperms received from the male Pila during copulation. Uterus :
Large yellow and pear shaped uterus lies below the intestine and to the right of the renal chamber. It communicates receptaculum seminis to the vagina. Vagina :
A white cream – coloured tubular vagina runs along the left side of the rectum in the branchial chamber.
It opens outside a little behind the anus through female genital aperture situated on a small papilla.

7. Copulatory apparatus: A rudimentary penis lies beneath a glandular fold of the mantle. It is a thin flagellar structure nearly 6.0mm long and pointed at the tip. Hypobranchial gland: In female it is poorly developed with a rudimentary glandular thickening.

8. Breeding and development Breeding in Pila takes place in the rainy season. It involves three processes: copulation, fertilization and laying. Copulation : Copulation may occur in water on moist land. It takes about 3-4 hrs. The male and female snails come together facing one another with their right nuchal lobes lie opposite to one another. The penis of the male elongates along with its sheath and its proximal end comes in contact with the male genital aperture and the distal end passes into the mantle cavity of the female and finally to its genital aperture. Now the seminal fluid is shed into the vagina of the female where it migrates to be stored into the receptaculum seminis . After that, both separates Fertilization : Fertilization is internal in Pila. It takes place in the uterus, where both ova and spermatozoa pass, the former from the ovary and the latter from the receptaculum seminis . Laying : Egg laying starts 2 or 3 days after copulation. The eggs are laid in sheltered places (holes and crevices) or moist land near water. A single female lays 200-800 eggs at a time. The eggs are rounded, about the size of the pea seeds and covered by whitish shell. They contain a good deal of food.

9. development Development occurs out­side the body of the female. The parents do not incubate or look after the eggs. Development of Pila is direct. The embryo floats in a central core of liquid albumen which is surrounded by a thick layer of whitish solid albumen.

During development the visceral mass and the shell of the embryo becomes spirally coiled and the characteristic phenomena of torsion takes place. This results in the asymmetry of the body. The young snails hatching from the eggs are similar in form to the adult.