In some dictionaries you won’t find anything if you don’t search for the plural of “bourse“.

It’s a relatively “noble” term to say the scrotum, better that “testicules” or any other less courteous synonym.

This text relates to a very distant past (here).

It appears to relate to a primitive time, when music was done by simple means like singing and clapping hands, so arguably when clothing was minimal, and money and purses were still lying in the future.

So bourses here is likely used in its acceptation of scrotum, though its plural form, in the per person count of objects (deduced from only one sexe being mentioned), would more likely point out at the testicles (through a metonymy?).

Alors ils essuyaient sur le sol les traces de leurs bourses et de leur sexe qui s’y étaient déposées.

Then they were wiping off from the ground the marks left by their scrotum and sex.

_{Note that déposées is feminine, and though bourses is also feminine, sexe is not, so if déposé was related to the bourses and sexe, it should have been masculine (déposés). Therefore, déposées relates to traces, but in my understanding, traces are not déposées, unless some paint or other substance is added to the object receiving the traces, which is likely not the case here¹. It might be some stylistic figure I don’t understand, but I left it out altogether from my translation, because I am too unsure and it doesn’t appear mandatory or even relevant when linked with traces.}

_{¹ …though someone insisted down in the comments that the spreading of sperm on the ground was the only acceptable interpretation. I am not at all convinced of this, since the feminine mark on déposées is, as far as I can tell, the only hint that something like this might be happening. In the whole first chapter I could find nothing else related to having sex. However, I might be too naive to spot the images.}