Until 1934 the life history of Syngamus trachea was usually considered to be direct though Walker in 1886 and Waite in 1920 had both tentatively suggested that earthworms play a part in the dissemination of the parasite. In that year, however, I was able to show conclusively in this laboratory that the rôle they play in transmitting the nematode is a very important one, for by means of this annelid it was possible to effect with certainty heavy infections in various birds of domestic importance. The following year it was shown also that Syngamus from starlings can easily be transmitted to chickens by earthworms: this method apparently overcomes the resistance due to a different “host strain” such as Taylor had previously encountered when he tried to infect chickens directly with material obtained from starlings. In 1938 using earthworms as vectors chickens, pheasants and partridges were easily given definite infections with various other “strains” of Syngamus. Consideration of these results made it no longer possible to ignore the importance of earthworms in the life cycle of “Gapes.”