CESOPHAGUS, STOMACH, AND INTESTINE 259 



branchs, Ganoids, and Dipnoans, the fold 

 and forms a well-marked spiral valve, the 

 turns of which may lie so close together 

 as to almost fill the cavity of the intestine 

 (Figs. 206, 207, 209). In the Ganoids it 

 begins to undergo degeneration ; thus in 

 Lepidosteus (Fig. 207) it is only present 

 in the hinder part of the intestine. 

 Traces of a spiral valve can even be re- 

 cognised amongst the Teleostei (Cheiro- 

 centrus and possibly certain Salmonidse). 



Pyloric cceca are met with in Ganoids 

 and numerous Teleosts, and consist of 

 longer or shorter finger-shaped processes 

 of the small intestine, situated posteriorly 

 to the pylorus in the region of the bile- 

 duct (Figs. 207 and 208). Their number 

 varies from 1 (Polypterus and Ammo- 

 dytes) to 191 (Scomber scomber). The 

 pyloric caeca and spiral valve seem to have 

 a similar function, and, as a general rule, 

 to be developed in inverse proportion to 

 one another. 



In the narrow-bodied Gymnophiona 

 the intestine is only slightly coiled, while 

 in Anura it becomes considerably folded 

 on itself: its form in Salamanders is about 

 mid- way between these two extremes. 



In the Cyclostomi, Holocephali, 

 Ganoidei, and most Teleostei, there is 

 a separate anus ; in all other Fishes as 

 well as in the Dipnoi and Amphibia the 

 large intestine opens into a cloaca common 

 to it and to the urinogenital ducts. The 

 large intestine (rectum) is comparatively 

 short and takes a straight course; in 

 Amphibians, as well as to some extent 

 in certain Ganoids and Teleosts, it is 

 plainly marked off from the small 

 intestine, and between the two there is 

 often a circular valve. In some cases 

 the rectum is considerably swollen and 

 may even exceed the stomach in cap- 

 acity (Fig. 210, B\ An outgrowth of 

 the ventral wall of the cloaca in Am- 

 phibia gives rise to the urinary Uadder, 

 and represents the allantow (p. 9) of 

 higher forms. 



is more highly developed 

 -a.V 



st 



FIG. 207. ALIMENTARY VIS- 

 CERA AND AIR-BLADDER OF 

 Lepidosteus, in situ. (After 

 Balfour and Parker. ) 



a, anus ; a. b, air-bladder ; 

 a. b ] , its aperture into the 

 throat ; b.d 1 , aperture of 

 bile-duct into intestine ; c, 

 pyloric cseca ; y.b, gall- 

 bladder ; hp.d, hepatic 

 duct ; lr, liver ; py, pyloric 

 valve ; *, spleen ; sp.v, spiral 

 valve ; st, stomach. 

 S 2 



