AND ON THE CLASSIFICATION OF FISH. 549 
a spiral valve in the intestine appear mutually dependent in the 
Selachii as in the Ganoids. We know of no exception. If we 
were acquainted with a Ganoid having a spiral valve in the in- 
testine, the arterial trunk and cardiac valves of which had not 
been examined, we might predict that it would possess a muscu- 
lar coat upon it and numerous rows of valves within. And, on 
the other hand, were we acquainted with the latter, but the in- 
testine had not yet been examined, we might predict with equal 
certainty that the spiral valve would be present. Lepidosiren is 
properly distinguished from the Ganoids. 
The sexual organs of the Ganoids are not formed on a com- 
mon plan; in this point of view there are indeed as well-marked 
differences among the Ganoids as among the families of the 
osseous fishes. In the Sturgeons and Polypterus the oviducts 
open into the abdominal cavity, and the ova are conveyed from 
the abdominal cavity through the infundibulum of the oviduct. 
Lepisosteus has abdominal apertures near the anus. The ova- 
ries are sacciform ; the ova are developed in the substance of the 
internal wall of the sac, which is continued into the oviduct. The 
oviducts do not proceed from the end but from the middle of 
the length of the sac, so that the sacs are blind anteriorly and 
posteriorly. The male generative organs do not present any 
peculiarities ; the seminal duct (vas deferens) in its course pre- 
sents some vesicular expansions, its ramification in the testes, 
and the whole testis may be inflated from the vas deferens. The 
vas deferens leads into the ureter. There is no true urinary 
bladder, but anterior to the orifice of the urogenital canal there 
is a considerable sacciform expansion, in which in the females 
the oviduct also terminates. The urinary bladder is also wanting 
‘in Polypterus. The reason why there are as great differences in 
the structure of the sexual organs of the Ganoids as between 
the families of the osseous fishes, is very interesting as regards 
the importance and the extent of the section which the Ganoids 
-taust form in a system. From this alone it is evident that they 
‘constitute far more than a family, and ¢hat their anatomical pe- 
culiarities cannot in any case be regarded as characters of a sepa- 
rate family of osscous fishes. Their location as a sub-class of 
‘the same rank as the Selachii, Osteacanthi, Cyclostomi and Si- 
renoidei is thus confirmed, and likewise the difference of family 
“between Lepisosteus and Polypterus is pointed out anew. 
_ The fissure of the retina of the eye and the falciform process 
2R2 
