466 Intestinal Folds and Villi in Vertebrates 



2. Both folds and villi in the same intestine. 



(a) With the folds net-formed. Gadow describes such a condition 

 in the Allida. I was unable to find such a condition in any forms 

 examined. 



(b) With zigzag folds and usually their plate-like villi regularly 

 arranged. Under this head come the mucosal elevations of Nydicorax 

 nycticorax, night heron, Scoter duck or Oidemia deglandi, Lars argen- 

 tatus smithsonensis, and a number of others. Gadow has described this 

 condition for Oriolus, Lanius, etc. 



3. Villi and no folds. 



(a) Some of the villi in parallel rows, or otherwise regularly arranged. 



In Flamingo, Owen, 69, described short villi in long parallel zigzag 

 rows. Similar conditions are described by Gadow, 49, in Scolapax/ 

 Limosa and others. In a specimen of domestic duck some conditions 

 were noticed which differ in several respects from any other form 

 studied and so will be given in more detail. 



Domestic duck.— In the upper part of the intestine of duck, the villi 

 are quite regular and numerous. They are thin at first, square for 

 the first part of their length, but near the tips, triangular shaped with 

 sharp points. In many cases, two villi fit together; on one side the 

 outer edge of one is thickened and each thick edge laps upon the thin 

 edge of the other (Fig. 43). The villi are in quite close contact 

 throughout their whole extent. This pointed sort of villus extends 

 down the intestine for about 82 cm. and they are about 1.2 mm. high 

 by .3 mm. broad at the base. There are about 12 villi to the sq. mm. 

 For the last 63 cm. of the small intestine the villi become quite imi- 

 formly .6 mm. high by .3 mm. broad. They are thin, oblong plates 

 with even edges and right angles. These villi are arranged very regu- 

 larly and there are about 15 to the sq. mm. Upon looking down upon 

 the surface of the intestine, it is seen that each side of the top of each 

 one has presented to it the edge of the top of another villus (Fig. 44). 

 In the caeca, the villi are somewhat smaller and elongated, .4 mm. by 

 .15 mm. broad at the base (Fig. 45). In the large intestine, the villi 

 are thin plates that have straight edges with right angles and are 

 screen shaped. Each top looks like a broadened "v" when looking 

 directly down uppn it. These villi are about .6 mm. high by .8 mm. 

 broad and are arranged in regular, parallel rows, the convexity of one 

 villus fitting into the indentation of the other (Fig. 46). There are 

 four or five of these to the sq. mm. In each caecum there are about 

 7500 villi; in the large intestine about 16,000; in the small intestine, 

 440,000, or nearly 500,000 in all. 



