In 1909, the writer collected egg-masses of the seroot Tabanus taeniola, P. de B., and reared some of the resulting larvae to approaching maturity, but failed to obtain the pupa. The following year he took a number of immature larvae of Tabanus ditaeniatus, Macq., and reared them to the adult stage. The various stages in the life-cycles of these two Tabanids, with the exception of the pupa of the former and the egg-mass of the latter species, were figured and described in this Bulletin. The puparium of T. taeniola and egg-masses of T. ditaeniatus which are here figured and described were obtained during the summer of 1913.