AND ON THE CLASSIFICATION OF FISH. 515 
of the porus uro-genitalis in both animals, as ia the osseous 
fishes, and different from the cloaca of the Plagiostomi. 
The Ganoidei approach the Plagiostomi in the formation of 
the alimentary canal, for Acipenser and Polyodon have a spi- 
ral valve in the intestine, as in the Sharks and Rays, and in 
Polypterus it has been described by its discoverer, but no osse- 
ous fish possesses such a structure. The spiral valve, however, 
is not universal among the Ganoids, for it has not been shown 
to exist in Lepisosteus. The intestine of the Plagiostomi and 
Polypterus is formed on the same plan. The tube which ascends 
from the sacciform stomach, which in this instance passes off 
laterally, extends as far as the valvular intestine, where we first 
meet with the pylorus. This tube is therefore not an intestine, 
as Geoffroy St. Hilaire called it, but the ordinary pyloric canal, 
the “ branche montante” of the stomach. At the upper rounded 
end of the valvular intestine of the Plagiostomi a valveless cavity 
exists between the commencement of the valve and the pylorus. 
This is the bursa Entiana; it receives the biliary and pancreatic 
ducts, and also in the foetus the ductus vitello intestinalis; it is 
undoubtedly that portion of the small intestine which most 
nearly resembles the duodenum. If the valvular intestine be 
considered as the colon, this would receive nothing more from 
the small intestine than the Jursa Entiana, which is absurd. The 
entire valvular intestine with the dursa ought rather to be con- 
sidered as the small intestine, and the valveless end of the rectum 
alone as analogous to the large intestine. In the osseous fishes, 
likewise, the canal is not divided into small and large intestine, 
but into small intestine and rectum. The intestinal canal of 
Polypterus may be explained in this manner, or rather the intes- 
tine of this Ganoid itself confirms this view. In Polypterus a 
bursa is barely perceptible, and the valve of the valvular intestine 
arises from the circumference of the pyloric infundibulum. Near 
this spot the intestine expands into the blind, sacciform ap- 
pendage, called the appendix pylorica, and the biliary duct also 
opens near the pylorus. Had Geoffroy St. Hilaire sought for 
or known this orifice, he would not have considered the pyloric 
duct of the stomach as the small intestine. 
The Sturgeons differ from Polypterus merely in the form of 
the stomach, and in the development of the space between the 
valve and pylorus or the bursa of the Plagiostomi, which forms 
a complete flexure, the duodenal loop of the intestine. Their 
VOL. IV. PART XVI. arp 
