The following are the more important facts which are known about the generative and urinary ducts of Ganoids. In Spatularia (vide Hyrtl, Geschlechts u. Harnwerkzeuge bei den Ganoiden, _Denkschriften der k. Akad. Wien_, Vol. VIII.) the following parts are found in the female. (1) The ovaries stretching along the whole length of the abdominal cavity. (2) The kidneys, which are separate and also extend along the greater part of the abdominal cavity. (3) The ureters lying on the outer borders of the kidneys. Each ureter dilates at its lower end into an elongated wide tube, which continues to receive the ducts from the kidneys. The two ureters unite before terminating and open behind the anus. (4) The two oviducts (Müllerian ducts). These open widely into the abdominal cavity, at about two-thirds of the distance from the anterior extremity of the body-cavity. Each opens by a narrow pore into the dilated ureter of its side. In the male the same parts are found as in the female, but Hyrtl found that the Müllerian duct of the left side at its entrance into the ureter became split into two horns, one of which ended blindly. On the right side the opening of the Müllerian duct was normal. In the Sturgeon (vide J. Müller, _Bau u. Grenzen d. Ganoiden_, Berlin Akad. 1844; Leydig, _Fischen u. Reptilien_, and Hyrtl, _Ganoiden_) the same parts are found as in Spatularia. The kidneys extend along the whole length of the body-cavity; and the ureter, which does not reach the whole length of the kidneys, is a thin-walled wide duct lying on the outer side. On laying it open the numerous apertures of the tubules for the kidney are exposed. The Müllerian duct, which opens in both sexes into the abdominal cavity, ends, according to Leydig, in the cases of some males, blindly behind without opening into the ureter, and Müller makes the same statement for both sexes. It was open on both sides in a female specimen I examined[37], and Hyrtl found it invariably so in both sexes in all the specimens he examined. Footnote 37: For this specimen I am indebted to Dr Günther. Both Rathke and Stannius (I have been unable to refer to the original papers) believed that the semen was carried off by transverse ducts directly into the ureter, and most other observers have left undecided the mechanism of the transportation of the semen to the exterior. If we suppose that the ducts Rathke saw really exist they might perhaps be supposed to enter not directly into the ureter, but into the kidney, and be in fact homologous with the vasa efferentia of the Selachians. The frequent blind posterior termination of the Müllerian duct is in favour of the view that these ducts of Rathke are really present.