it is possible that others are similarly affected. And it is highly important to note the prevalent habit among the Tubificidae of lying with the head end imbedded in the mud of the pool which they inhabit, while the tail end emerges and waves freely in the flood. The additional fact that this tail end occasionally bears gills (as in _Branchiura sowerbii_ and _Phreodrilus branchiatus_) has a collateral importance not to be mistaken. CHAPTER V RELATIVE FREQUENCY OF EARTHWORMS IN DIFFERENT REGIONS OF THE WORLD It will be of use for various purposes to be considered later to arrive at a comprehensive view of the relative numbers of species and genera of earthworms in the four quarters of the globe. And in making this general census we shall not take into consideration the purely aquatic forms, but shall limit ourselves to the earthworms, _sensu stricto_, or Megadrili, of which, however, it is true that some members are actually lake and river dwellers. This latter fact will not, however, interfere with the usefulness of the comparative survey. Two preliminary remarks are necessary. The opinions of naturalists vary as to the limits of genera; and a species may be a species to one and a mere variety to another. Thus it will be impossible to give a summary of the facts to be enumerated presently, which will be either absolutely accurate or which will satisfy everyone in every detail. But it is asserted that the following survey is substantially correct. In the second place it is often possible to eliminate from the fauna of a given region those species and even genera which have been accidentally imported, a matter which will receive careful consideration on a later page. Such forms are therefore, in those cases at any rate where the evidence seems to be overwhelming, withdrawn from the list. In other cases, particularly in the Eastern region of the world, it has been found less easy to rectify the catalogues by removing what Dr Michaelsen has termed 'peregrine' forms. We shall commence with a census of South America; the entire Continent will be divided for the present purpose into three divisions, viz. South America, Central and North America, and in the third place the West Indian Islands. In South America we find that the bulk of the indigenous earthworms belong to the family Geoscolecidae and to a definite sub-family, viz. Geoscolecinae. These genera are _Onychochaeta_ with one species, _Hesperoscolex_ of which one species is known from the area, _Periscolex_ with one species, _Anteoides_ with two species, _Pontoscolex_ one species. _Opisthodrilus_ with two species, _Rhinodrilus_ (including either as synonyms or as sub-genera, _Thamnodrilus_, _Anteus_, _Tykonus_, _Urobenus_ and _Aptodrilus_) with no less than 49 species: _Andiodrilus_ with five species, _Holoscolex_ with one species, _Glossoscolex_ ten species, _Fimoscolex_, _Andiorrhinus_ and _Enantiodrilus_ with one species apiece.