AND ON THE CLASSIFICATION OF FISH. 513 
in the case of the true osseous fishes. The existence of the 
blowing-hole in Polypterus was an incomprehensible fact so long 
as it was considered as an osseous fish. Now, since it has been 
proved that the Sturgeons and Spatularie are most closely re- 
lated to it, the reverse happens; it rather requires to be explained 
why these openings, which appear to be so essential to the con- 
stitution of a Ganoid, are absent in Lepisosteus. I believe that 
they occur in it in the foetal state, just as I found them’ in the 
foetus of those genera of Sharks, in the adult state of which they 
are absent (Carcharias). 
The swimming-bladder is present in all the living Ganoids, 
as well as the Sturgeon and Polyodon; it is furnished with an 
air-duct, but not with a rete mirabile, as in the Abdominal Ma- 
lacopterygians, or more certainly the Physostomi, among the 
osseous fishes. 
The relations of the sexual organs in the Ganoids are very 
peculiar. The account of the sexual organs of Polypterus in 
the Description de V Egypte, is imperfect and partly incorrect; 
in pl. iil. fig. 7, ¢¢, the fatty valves of the chylopoetic viscera 
are mistaken for testicles. 
The ovaries of Polypterus lie anterior to the kidneys in the 
form of a long plate: each is attached to a mesentery. They 
have no internal cavity, and there is no outlet from them except 
into the abdominal cavity, as we find in the Plagiostomi, the 
Sturgeons, Cyclostomi, and a few osseous fishes, such as the 
Kel and Salmon. The ova are conveyed from the abdomen 
through true oviducts. This entirely separates Polypterus from 
the osseous fishes, also from those last-mentioned, in which there 
is a mere abdominal aperture without any oviduct; it rather ap- 
proximates to those fishes which have separate oviducts, viz. the 
Plagiostomi, Sturgeons and Lepidosirens. The form of the ovi- 
duct most nearly resembles that of the Sturgeons. 
In Polypterus the oviducts are situated exactly in front of the 
long and broad urinary tubes, and are united to them by fibrous 
tissue ; they open into the abdominal cavity at the distance of a 
few inches from the anus, by a broad transverse slit. This ori- 
fice lies close to the ovarian mesentery, externally to its under 
side. The oviduct and ureter follow their course, remaining 
separate until just before the common termination in the uro- 
genital pore behind the anus. If we inflate the latter, the ureters 
become gradually filled with air, sometimes also the oviducts. 
