The Mermithidae are a well-defined phylogenetic group of parasitic nemas, usually ranked as a family. Investigations now under way in the U. S. Department of Agriculture indicate the existence of hundreds of species belonging to a considerable number of genera which, during some stage of their development, are largely parasites of invertebrates. This paper deals primarily with observations on Mermis subnigrescens Cobb, 1925, and Agamermis decaudata Cobb, Steiner, and Christie, 1923, two of the few species of which the compete life-cycles are fairly well known. The information here recorded was not obtained as the result of a systematic effort to study the problem of sex determination in this group, but came more or less incidentally in connection with studies on life-histories and certain economic phases of the mermithid problem.
AOAMERMIS DECATJDATA, A STRICTLY BISEXUAL SPECIES
A brief account of the life-cycle of A. decaudata has already been published (Cobb, Steiner, and Christie, '23). Females have a length of from 50 to 465 mm. (the larger sizes being more common), while the males .are considerably smaller, 'The writer is indebted to Miss Gertrude L. Power, Division of Nematology, Bureau of Plant Industry, for faithful assistance in carrying on the experiments and in preparing the drawings and manuscript, and to MI. A. N . Caudell, Bureau of Entomology, for the identification of the host insects.