Within the limits of the same sub-family as that which contains _Notiodrilus_, _i.e._ the Acanthodrilinae, the changes of structure affect all the principal organs of the body except the nervous system, but are not very large and vary from genus to genus. They are mainly perhaps in the direction of reduction and simplification. Thus in _Chilota_, _Maheina_ and _Yagansia_ the spermaries are reduced to one pair in either the Xth or XIth segment, while in _Yagansia_ one pair of spermathecae and of spermiducal glands have also disappeared. In _Microscolex_ the spermaries remain normal, but one pair of spermathecae and of spermiducal glands have disappeared, the remaining organs of these series being in the IXth and XVIIth segments respectively. In _Microscolex_, _Chilota_ and _Yagansia_, moreover, there is a further degeneration in the disappearance of the calciferous glands. These glands are often absent and sometimes less developed in the New Zealand _Maoridrilus_, which is otherwise not a degenerate form and differs characteristically from _Notiodrilus_ by the fact that the paired nephridia alternate in position in successive segments, being now in front of the dorsal, and in other segments in front of the ventral, pairs of setae. While these genera are somewhat degenerate, the New Zealand _Plagiochaeta_ has undergone specialisation in an upward direction. For the setae of each segment are increased to a large number much exceeding eight. It is not a long step to the sub-families Diplocardiinae and Trigastrinae. In the first of these, an American race confined to the northern and central parts of that continent, the male pore shows a tendency to move backwards, being situated on any of segments XVIII-XXI. The two spermiducal glands follow it, but are always placed one pair in front and one behind, as in _Notiodrilus_. In this group we get a new feature of specialisation in the duplication or triplication of the gizzard. So too with the Trigastrinae where there are either two or three gizzards; but in this sub-family another modification has become apparent. The paired nephridia have disappeared and their place is taken by several, often quite numerous, pairs of much smaller nephridia called on that account 'micronephridia' instead of 'meganephridia.' To this sub-family belong the especially African but also American and Malayan _Dichogaster_, whose name is derived from the important fact that it possesses two gizzards.