Sentence:  The eggs [of a lancet fluke ("Dicrocoelium dendriticum")] that pass out with the manure of an infested sheep do not hatch in the open. When eaten by the snail, they hatch and finally give rise to larvae that pass out of the snail's body in gelatinous "<WSD>slime</WSD>[-]<WSD>balls</WSD>." 
Meaning of the word marked with <WSD> tags:  A mucus-coated lump containing the (parasitic larvae) of a liver fluke (of the phylum Platyhelminthes).