Seed Saving from Courgettes
Pumpkins, squashes, marrows & courgettes will all cross readily with each other. The best (usually only) way to save pure seed on a home scale is to hand pollinate one or more fruits.
Plants have two different types of flower, male and female. Only female flowers will grow into gourds. Female flowers have small immature fruit beneath the flower. Male flowers just have a straight stem. You need to transfer pollen from a male flower into a female flower, making sure that no pollen gets introduced from plants of a different variety.
There are detailed instructions later in these instructions
Allow the fruit to develop, then harvest and keep in a cool dry place for another month or so to ripen further.
Then cut the fruit in half, and scoop out the seeds, leaving the rest of the fruit for cooking as normal.
Wash the seed in a colander, rubbing it between your hands to get rid of the fibres, and then shake off as much water as possible. Spread the seed out on a plate to dry. Seeds need to dry as quickly as possible, but without getting too hot, for example, dry on a sunny windowsill.
To test whether the seeds are dry enough, try bending one in half. If it is dry, it will snap rather than bending.