It proves in the first place that the transportation outwards of the genital products of both sexes by homologous ducts, which has been hitherto held to be universal in Ganoids, and which, in the absence of evidence to the contrary, must still be assumed to be true for all Ganoids except Lepidosteus, is a secondary arrangement. This conclusion follows from the fact that in Elasmobranchii, &c., which are not descendants of the Ganoids, the same arrangement of seminal ducts is found as in Lepidosteus, and it must therefore have been inherited from an ancestor common to the two groups.
If, therefore, the current statements about the generative ducts of Ganoids are true, the males must have lost their vasa efferentia, and the function of vas deferens must have been taken by the homologue of the oviduct, presumably present in the male. The Teleostei must, moreover, have sprung from Ganoidei in which the vasa efferentia had become aborted.
Considerable phylogenetic difficulties as to the relationships of Ganoidei and Elasmobranchii are removed by the discovery that Ganoids were originally provided with a system of vasa efferentia like that of Elasmobranchii.
[537] Treatise on Comparative Embryology, Vol. I., p. 43 [the original edition].
[538] The females we examined, which were no doubt procured at the same time as the male, had their oviducts filled with ova: and it is therefore not surprising that the vasa efferentia should be naturally injected with sperm.
[539] The change is probably effected somewhat earlier than would appear from our description, but our specimens were not sufficiently well preserved to enable us to speak definitely as to the exact period.
[540] We feel fairly confident that there is only one pronephric opening on each side, though we have no single series of sections sufficiently complete to demonstrate this fact with absolute certainty.
[541] Rosenberg, Untersuch. ueb. d. Entwick. d. Teleostierniere, Dorpat, 1867.
[542] Götte, Entwick. d. Unke, p. 826.
[543] Sedgwick, “Early Development of the Wolffian Duct and anterior Wolffian Tubules in the Chick; with some Remarks on the Vertebrate Excretory System,” Quart. Journ. of Micros. Science, Vol. XXI., 1881.