William A. Hilton 465 



pean species and found in American forms are either somewhat net- 

 formed, or much like those of Necturus, Amblystoma, etc., but may be 

 larger and slightly more wavy. 



Villi have been described by Langer, 86, in the genus Bufo; these 

 villi are said to be long and overlap each other; but in Bufo agua Klein, 

 50, described net-formed folds. In Bufo lentiginosus americanus, I 

 found a net arrangement of folds for a short distance beyond the 

 pyloric valve. Isolated parts of these folds approximate villi (Fig. 9). 



There are a few descriptions of villi in reptiles. Meckel, 17 and ig, 

 has described villi in quite a number of forms and folds in some. 

 Stannius, 46 and 56, described villi in crocodiles and in ehamseleon. 

 In the American representatives of this class which were available for 

 study, no villi were seen and in the forms studied four different types 

 of folds were found : 



1. Long, plate-like, regular, parallel folds, which are rather thin, 

 but usually quite high and thickly placed. Such folds are found in 

 several species of turtles (Fig. 1). 



2. Parallel wavy folds, similar to those of Necturus, etc., such as are 

 found in some of the Colubridae and Crotalidse and some of the Lacer- 

 tilia. 



3. Very zigzag folds such as are found in Bascon constrictor (Fig. 8). 

 In this species, the common blacksnake, besides these very zigzag folds, 

 areas were found where the intestine either artificially or naturally, is 

 of small diameter and at these places the zigzag folds are replaced by 

 parallel flat longitudinal plates or folds, 



4. Low, very zigzag elevations which differ from those of Cyprinidge 

 in being more prominent. In Alligator mississippiensis (Fig. 6) this 

 type of fold was found. 



The mucosal folds and villi of birds have received much attention 

 from Owen, 67, Gadow, 69-79, Eudolphi, 80, and a number of others. 

 The second of these authors quoted has done much more than any of 

 the others and the following types of structures found in American 

 forms correspond very closely to the structures given by Gadow for 

 European species. 



There are three of these divisions in which an attempt is made to 

 show the occurrence of folds and villi in birds. 



1. Folds and no villi. 



(a) Zigzag folds, such as are found in some of the sparrows and 

 described by Gadow in Monticola, Euphone, etc. 



(b) Net-arranged folds, as in Murre (Uria troile); and in the genus 

 Sturnus of Passeres described by Gadow. 



