LIFE CYCLE OF HIRUDINARIA/LEECH

- Hirudinaria is hermaphrodite but show cross fertilization.

- They copulate in water or on land especially during the months of March and April. Two leeches meet in such a way that male genital pore of each is opposite to the female genital pore of the other. Each copulant transfer spermatozoa by the penis into vagina of another leech i.e., they show reciprocal insemination. After about an hour copulants separate. 

- In Hirudinaria, fertilization takes place in the vagina and in the mean time ootheca formation starts during April-June. Clitellum becomes conspicous during ootheca formation. They secrete snow white girdle around clitellum i.e., segment 9 to 11 and clitellar gland produce albumen in the girdle. Now many fertilized eggs are laid into girdle through female genital pore.

- Leech now start withdrawing its preclitellar region from the anterior side of girdle. The prostomium glands secrete an anterior plug to close the anterior pole of the girdle. By further rhythmic contraction it brings prostomium close to the posterior pole of girdle which blocks this region by secreting posterior plug. Girdle now falls off and is called egg case or ootheca (30 x 15 mm). It is deposited by the worm in the moist place such as lumps of clay, sides of pond etc.

- Development of fertilized egg occurs in the ootheca. Once the development is complete, the polar plugs drop off and 1 to 24 leeches hatch from it.

- A larva cryptolarva develops within cocoon. It has protonephridia and a mouth to get nutrients within ootheca.

- Young leeches resemble the adult so metamorphosis occurs.