A flexible collapsible bag is introduced into the abdominal cavity to remove larger portions of tissue from the abdominal cavity through a threaded casing introduced into the abdominal wall. The bag has a side opening through which the tissue can be moved into the bag. The bag has an end opening which remains extracorporeal to the threaded casing in the abdominal wall. After partially pulling out the bag, the side opening is located outside of the threaded casing, and the tissue, which is tightly enclosed by the portion of the bag remaining in the abdominal cavity, is cut into pieces, as by cutting filaments having portions at the bottom of the bag and extending extracorporeally through the threaded casing and the end opening of the bag.