Dr Woodland kindly submitted to me the majority of the worms recovered by him on dissecting the mice used in his very interesting experiment (see his paper that follows), with a request for my opinion as to the identity of the species. The material, which was handed to me preserved in formalin, consisted only in part of complete specimens, a number of the worms having been broken up during collection. I stained most of the whole specimens with dilute haematoxylin and mounted them in Canada balsam. Upon microscopic examination it became evident that the specimens were of various ages and degrees of maturity, and one specimen was of exceptionally large size. This individual, in a fairly contracted condition, measures (after mounting and without stretching) 36 mm. in length, and has about 650 recognisable segments. Mature segments (i.e. segments with testes and ovary both fully developed) begin to appear-at about the 320th segment from the scolex, and gravid segments at about the 490th. There are thus about 160 gravid segments. It will be evident from these details that this specimen agrees with my description of “Hymenolepis longior.” Two of the young forms among Dr Woodland's material also seemed to agree with “H. longior” rather than with what I had regarded as H. nana.