Finally, we have the largest of all the sub-families of this family, viz. that of the Megascolecinae. These worms are mainly tropical in range and also mainly found in the Indo-Australian portion of the world. In them the sperm ducts open in common with the usually single pair of spermiducal glands and prevalently upon the XVIIIth segment. The glands moreover have not always, though they often have, the tubular form shown in all the sub-families hitherto considered. In many forms they are branched and lobate glands, and if there are two pairs one may be of one type and the other of the second and derived type, as for instance in _Megascolex ceylonicus_. Furthermore, it is much commoner among the genera of this sub-family for the setae to become numerous and to spread right round the segment; this condition is seen in the genera _Pheretima_, _Megascolex_, _Diporochaeta_, _Perionyx_, _Plionogaster_. The spermathecae also are commonly more than the typical two pairs of the forms already considered, and in certain species (for example _Pheretima hexatheca_) there are as many as six pairs of those organs which are moreover--and in this they resemble the majority of species of the last sub-families--nearly always furnished with a diverticulum or diverticula. The nephridia are either paired or numerous and these various characters allow of the sub-family being split up into sixteen genera or thereabouts. As an example of another type of organisation and as contrasting with _Notiodrilus_ we may now briefly describe the structure of the genus _Pontoscolex_ (better known as _Urochaeta_), a member of the American and African family Geoscolecidae.