|Left: A pair of mating leech. Right: Leeches riding on the legs of a crab (from Fig. 1 of the paper)|
|Top: Leech with spermatophore attached|
Middle: Leech with filled brood pouch
Bottom: Young leeches emerging
from brood pouch
From Fig. 2 of the paper
If the prospect of being harpooned with a sperm-filled syringe is not daunting enough, the recipient also make a habit of collecting a bunch of spermatophores from a number of different depositors, probably to ensure they can have the cream of the crop (so to speak). Once the spermatophore has made its mark, the sperm it carries are able to make their own way to the egg, no matter where the spermatophore may have initially landed on the leech's body. At this point it is not entirely clear how they accomplish this.
Once the eggs are fertilised, the sperm recipient, now playing the role of mother leech, transfer the eggs (which can be as many as 50) to a brood pouch in her belly (which is where the name kangaroo leech came from). There they will be protected and nurtured. Once the eggs hatch, the baby leeches continue to receive nutrient from their mother through her body wall and into their posterior suckers. Those developing leeches will stay in the pouch for four weeks. As a final send-off, the mother leech will find an unsuspecting clawed frog, and the young leeches are "released explosively" over the surface of the frog, thus ensuring that those blood-suckers will get the best possible start to their own lives.
Marsupiobdella africana - a loving and nurturing blood-sucker which wants nothing but the best for its babies (see also another blood sucker which goes to great lengths to care for its brood here).
Kruger, N., & Du Preez, L. (2015). Reproductive strategies of the kangaroo leech, Marsupiobdella africana (Glossiphoniidae). International Journal for Parasitology: Parasites and Wildlife 4: 142-147.