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embryo Lepidosteus is homologous with the structure to which the 
same name is given in an embryo Elasmobranch, such as Scyllium or 
Torpedo. I have described for Lepidosteus a very similar origin and 
extension of the pronephros — over from three to six segments, usu- 
ally three — to that ascribed to it in Zlasmobranchü by RÜcKERT 
and VAN WIJHE, and by Kuprrer in Petromyzon. It is not necessary 
here to deal with the matter in detail. The greatest extension appears 
to be over six segments. 
BALFOUR !) concluded that in Ganoidei and Teleostei the pro- 
nephros must be considered as a larval structure — an organ func- 
tional in the larva — and pointed out that in the adult it degenerates 
into a mass containing lymphoid tissue. 
In fine, in Marsipobranchii?), Ganoidei and Teleostei 
the pronephros is undoubtedly completely degenerated in the adult; 
and it follows, as a matter of course, that no homologue of the Müllerian 
duct and its ostium abdominale, derived from the pronephros is or can 
be formed in any of the three sub-classes. 
Moreover, we possess no researches on these forms which. entitle 
us to say that the pronephros at any time in the history of the in- 
dividual makes the slightest attempt to develop any part of a Mül- 
lerian duct apparatus. For BALFOUR and PARKER?) found that the 
anterior part of the oviduct of Lepidosteus arises as a fold of perito- 
neum, and not from any part of the pronephros. 
Acipenser resembles Lepidosteus so closely in its development, as 
will be presently shown, that I shall not be far wrong, if I assume 
a similar mode of origin for the oviduct of Acipenser. 
So we arrive at this conclusion: that in Marsipobranchii, 
Ganoidei and Teleostei the pronephros enters into no relation- 
ships at any time with the generative organs, that no Miillerian duct 
is formed, and that the ova are conveyed to the exterior by means 
of abdominal pores, or of modifications of such pores. On the other 
hand, that in Selachii, Dipnoi and Amphibia the pronephros 
becomes modified for the service of the female generative organs, pori 
abdominales are present, more usually inconstant or absent, but if 
1) Batrovr, F. M., On the nature of the organ in adult Teleosteans 
and Ganoids, which is usually regarded as the head kidney or pro- 
nephros. Quart Journ. Micros. Sci. 1882. 
2) Myxine hardly forms an exception, but the organ here requires 
re-investigation. At any rate, it forms no Miillerian duct apparatus. 
3) Batrour and Parker, On the structure and development of Le- 
pidosteus. Phil. Trans. Roy. Soc. Lond. Part II, 1882, p. 421. 
