413 
MESSRS. F. M. BALFOUR AND W. N. PARKER OK THE 
fact that the ovary is already developed, and not only so, but the formation of the 
oviducts has commenced, and their condition at this stage throws considerable light 
on the obscure problem of their nature in the Ganoids. 
Unfortunately, the head of the young Fish had been removed before it was put into 
our hands, so that it was impossible for us to determine whether the pronephros was 
still present; but as we shall subsequently show, the section of the segmental duct, 
originally present between the pronephros and the front end of the permanent kidney 
or mesonephros, has in any case disappeared. 
In addition to an examination of the excretory organs in situ , which showed little 
except the presence of the generative ridges, we made a complete series of sections 
through the excretory organs for their whole length (Plate 26, figs. 54-57). 
Posteriorly these sections showed nothing worthy of note, the excretory organs and 
their ducts differing in no important particular from these organs as we have described 
them in the adult, except in the fact that the segmental ducts are not joined by the 
oviducts. 
Some little way in front of the point where the two segmental ducts coalesce to 
form the urinary bladder, the genital ridge comes into view. For its whole extent, 
except near its anterior part (of which more hereafter) this ridge projects freely into 
the body-cavity, and in this respect the young Fish differs entirely from the adult. As 
shown in Plate 26, figs. 56 and 57 (g-r.), it is attached to the abdominal wall on the 
ventral side of, and near the inner border of each kidney. The genital ridge itself 
has a structure very similar to that which is characteristic of young Elasmobranchii, 
and it may be presumed of young Fishes generally. The free edge of the ridge is 
swollen, and this part constitutes the true generative region of the ridge, while its 
dorsal portion forms the supporting mesentery. The ridge itself is formed of a central 
stroma and a germinal epithelium covering it. The epithelium is thin on the whole 
of the inner aspect of the ridge, but, just as in Elasmobranchii, it becomes greatly 
thickened for a band-like strip on the outer aspect. Here, the epithelium is several 
layers deep, and contains numerous primitive germinal cells ( p.o .). 
Though the generative organs were not sufficiently advanced for us to decide the 
point with certainty, the structure of the organ is in favour of the view that this 
specimen was a female, and, as will be shown directly, there can on other grounds be 
no doubt that this is so. The large size of the primitive germinal cells (primitive ova) 
reminded us of these bodies in Elasmobranchii. 
In the region between the insertion of the genital ridge (or ovary, as we may more 
conveniently call it) and the segmental duct we detected the openings of a series of 
peritoneal funnels of the excretory tubes (Plate 26, fig. 57, p.f.), which clearly there- 
fore persist till the young Fish has reached a very considerable size. 
As we have already said, the ovary projects freely into the body-cavity for the 
greater part of its length. Anteriorly, however, we found that a lamina extended 
from the free ventral edge of the ovary to the dorsal wall of the body-cavity, to which 
