A wellstring assembly comprising a tubular first wellstring part with a passageway; a second wellstring part co-operating with the first wellstring part; and a releasable wellstring-interconnecting means for selectively interconnecting the first and second wellstring parts; an auxiliary tool for manipulating the second wellstring part, which auxiliary tool can pass along the passageway in the first wellstring part to the second wellstring part, comprising a tool-connecting means for selectively connecting the auxiliary tool to the second wellstring part, and an operating means for operating the wellstring-interconnecting means.