Sentence:  Even so, Redi retained a belief that in certain other cases—the origin of parasites inside the human or animal body or of grubs inside of oak <WSD>galls</WSD>—there must be spontaneous generation. Bit by bit the evidence grew against such views. In 1670 Jan Swammerdam, painstaking student of the insect's life cycle, suggested that the grubs in <WSD>galls</WSD> were enclosed in them for the sake of nourishment and must come from insects that had inserted their semen or their eggs into the plants. 
Meaning of the word marked with <WSD> tags:  A blister or tumor-like growth found on the surface of plants, caused by burrowing of insect larvae into the living tissues, especially that of the common oak gall wasp (noshow=1).