It is perhaps unnecessary to introduce this series of papers with the remark that the chief interest in the study of the Mallophaga centres about the problems associated with their distribution and that these problems are in some measure at least coincident with the problem of the genetic relationship of their hosts. All this has been said very clearly, many times and by various writers. Yet I repeat it again, for it is this interest which is responsible for the papers to follow and it is as a contribution toward the study of these problems that they are intended, notwithstanding the circuitous route that may be followed in arriving at this goal.