To sum up, they appear for the most part to pertain to the Malay races.

I may add that the Count d'Artigas certainly belongs to that particular race which peoples the Dutch isles in the West Pacific, while Engineer Serko must be Levantine and Captain Spade of Italian origin.
But if the inhabitants of Back Cup are not bound to each other by ties of race, they certainly are by instinct and inclination.

What forbidding, savage-looking faces they have, to be sure! They are men of violent character who have probably never placed any restraint upon their passions, nor hesitated at anything, and it occurs to me that in all likelihood they have sought refuge in this cavern, where they fancy they can continue to defy the law with impunity, after a long series of crimes--robbery, murder, arson, and excesses of all descriptions committed together.

In this case Back Cup is nothing but a lair of pirates, the Count d'Artigas is the leader of the band and Serko and Spade are his lieutenants.
I cannot get this idea out of my head, and the more I consider the more convinced I am that I am right, especially as everything I see during my stroll about the cavern seems to confirm my opinion.
However this may be, and whatever may be the circumstances that have brought them together in this place, Count d'Artigas' companions appear to accept his all-powerful domination without question.

On the other hand, if he keeps them under his iron heel by enforcing the severest discipline, certain advantages, some compensation, must accrue from the servitude to which they bow.