FAM. 3. _Discodrilidae._[432]—This family consists of small parasitic forms which were at one time assigned to the Hirudinea; there seems, however, to be no doubt that they are rightly included in the present Order. _Branchiobdella_ is found upon the gills of the Crayfish, _Astacus fluviatilis_; the American _Bdellodrilus_ upon _Cambarus_. The chief reason for the former inclusion of these worms among the leeches was due to the absence of chaetae and to the presence of chitinous jaws and of suckers; apart from these structures there is nothing whatever leech-like about the worms. _Bdellodrilus_ has two pairs of testes in segments 5 and 6; there are two pairs of sperm-ducts, all opening, however, by a common "atrium" on the sixth segment; on the fifth open a pair of spermathecae, likewise by a common pore. The ovaries are in segment 7, and the ova escape by a pair of pores apparently like the single pore of the Enchytraeidae. The entire worm consists of only eleven segments. FAM. 4. _Phreoryctidae._[433]—This family contains only two {377}genera, _Phreoryctes_ and _Pelodrilus_. The former is widely spread, occurring in Europe, North America, and New Zealand. _Pelodrilus_ is limited to New Zealand. Most species of _Phreoryctes_ are distinguished by their extraordinary length and thinness, and there is frequently a tendency to the disappearance of the chaetae. The most important anatomical fact about _Phreoryctes_ (at any rate _P. smithii_) is that there are two pairs of ovaries as well as two pairs of testes, and that the ducts of all are simple and very much alike. This seems to argue the low position of the family in the series.