STRUCTURE AND DEVELOPMENT OF LEPIDOSTEUS. 
423 
undoubted Mullerian ducts, and could moreover easily be conceived as originating by a 
fold of the peritoneum, a slight extension of which would give rise to a genital duct 
like that of Lepidosteus. 
The main difficulty of the view that the genital ducts of Ganoids are not Mullerian 
ducts lies in the fact that they open into the segmental duct. While it is easy to 
understand the genesis of a duct from a folding of the peritoneum, and also easy to 
understand how such a duct might lead to the exterior by coalescing, for instance, with 
an abdominal pore, it is not easy to see how such a duct could acquire a communi¬ 
cation with the segmental duct. 
We do not under these circumstances wish to speak dogmatically, either in favour 
of or against the view that the genital ducts of Ganoids are Mullerian ducts. Their 
ontogeny would be conclusive on this matter, and we trust that some of the anatomists 
who have the opportunity of studying the development of the Sturgeon will soon let us 
know the facts of the case. If there are persisting funnels of the mesonephric segmental 
tubes in adult Sturgeons, some of them ought to be situated within the genital ducts, 
if the latter are not Mullerian ducts; and naturalists who have the opportunity ought 
also to look out for such openings. 
The mode of origin of the anterior part of the genital duct of Lepidosteus appears to 
us to tell strongly in favour of the view, already regarded as probable by one of us,* 
that the Teleostean genital ducts are derived from those of Ganoids ; and if, as appears 
to us indubitable, the most primitive type of Ganoid genital ducts is found in the 
Chondrostei, it is interesting to notice that the remaining Ganoids present in various 
ways approximations to the arrangement typically found in Teleostei. Lepidosteus 
obviously approaches Teleostei in the fact of the ovarian ridge forming part of the 
wall of the oviduct, but differs from the Teleostei in the fact of the oviduct opening 
into the kidney ducts, instead of each pair of ducts having an independent opening in 
the cloaca, and in the fact that the male genital products are not carried to the 
exterior by a duct homologous with the oviduct. Amia is closer to the Teleostei in 
the arrangement of the posterior part of the genital ducts, in that the two genital 
ducts coalesce posteriorly; while Polypterus approaches stiff] nearer to the Teleostei in 
the fact that the two genital ducts and the two kidney ducts unite with each other 
before they join; and in order to convert this arrangement into that characteristic of 
the Teleostei we have only to conceive the coalesced ducts of the kidneys acquiring 
an independent opening into the cloaca behind the genital opening. 
The male genital ducts. —The discovery of the vasa efferentia in Lepidosteus , carry¬ 
ing off the semen from the testis, and transporting it to the mesonephros, and thence 
through the mesonephric tubes to the segmental duct, must be regarded as the most 
important of our results on the excretory system. 
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 
* F. M. Balfour, ‘Comparative Embryology,’ veil, ii., p. 605. 
3 i 
MDCCCLXXXII. 
