1. An investigation has been made of the dependence on oxygen of some nematodes parasitic in the alimentary canal of sheep. Contrary to current conceptions it is shown that they are not anaerobic, and that all die within 48 hr. in the complete absence of oxygen. This is true of Ostertagia circumcincta and Trichostrongylus vitrinus even when arrangements are made--the apparatus is described--for any by-products of their metabolism which may permeate their cuticle to be removed from their environment.
2. A summary is given of the evidence in favour of the view that the metabolism of nematodes of the alimentary tract is aerobic.