Scole

From Earth Central

“	The scole clung to her chest, between and below her breasts, like a great flat aphid coloured in shades of dark brown and purple; however, it was a relatively small creature, as she was still a young woman. Observing a reddish flushing in the crevices between its many segments, as it rippled against her body, confirmed for her that it was drawing blood, and such a frequent feeding in the course of one day indeed meant it was preparing to litter.	„
—Line of Polity, Chapter 1

Scoles are a method of breathing in low-oxygen environments. Users must wear their scole for some time in an atmosphere with sufficient oxygen. When this oxygen is removed, the scole will re-oxygenate the host's blood and in turn take some of the host's blood. The host must regularly take anti-rejection pills for the scole to work, one of the factors keeping the population of Masada under the control of the Brotherhood (which had the only supply of anti-rejection pills available). Using a scole cuts the host's live expectancy in half. For this reason, most developed worlds no longer use them.

Eldene and her fellow workers wear scoles. Fethan, being a cyborg, does not need one, but wears a fake scole concealing tools to blend in on Masada.