A packaging bag for a liquid biological substance such as animal semen, including two walls made of plastic material joined in such a manner as to delimit a pouch for receiving the substance and, communicating with the pouch, an evacuation conduit whose end part, in the absence of opening of the bag, is closed by the joined walls, wherein, force-fitted in the conduit, a cannula being able to communicate with the pouch is provided, while a second end of the cannula is situated in the proximity of the end part of the conduit having a conical or substantially conical constriction, and wherein conduit communicates, over a part of its length, with at least one zone situated not far from the end part, in which the two walls are not joined.