464 Intestinal Folds and Villi in Vertebrates 



Besides the typhlosole of Petromyzon, simple longitudinal folds are 

 found in Cyclostomata; and the intestine of Myxine, according to J. 

 Miiller, 45, is entirely smooth except for a few very small longitudinal 

 folds. 



Villi have been described upon the spiral valves of Selachians by 

 Pillet, 85. My own observations seemed to confirm this description. 



In the intestines of Ganoids which I have been able to examine and 

 from descriptions by various investigators it seems evident that net- 

 like or zigzag, closely placed folds occur, but in Amia, the net-like fold 

 arrangement is in many places broken up into free projections which 

 are true villi (Hilton, 1900). 



Many varieties of mucosal elevations occur in different forms of 

 Teleosts. Villi have been described in Orthagoriscus mola by Kudolphi, 

 28, Owen, 68 ; Usox lucius, Grimm, 66. Meckel, 29, and Eatke, 37, have 

 also described villi in a number of species. In the rather limited num- 

 ber of Teleosts I have been able to examine, no true villi were found, 

 and in Esox lucius in which villi have been described, a simple network 

 of true folds was found which might be taken for villi in sections, but 

 could not otherwise be mistaken for them. 



Three forms of folds were found in Teleosts: 



1. The rather closely placed more or less wavy, thick folds; such as 

 Macallum, 84, describes for Amiurus catus and those found in Amiurus 

 nebulosus and Perca flavescens (Fig. 7). 



2. Very low zigzag folds which are scarcely more prominent than 

 those on the finger tips; such as those found in Oatostomus catostomus 

 one of the Catostomidse (Figs. 5 and 10), or those of Notropus cornutus 

 and Phimephales notatus of the Cyprinidge. 



3. Net arranged folds as those of Usox lucius. 



There seems to be very little literature upon the mucosal elevations 

 of Dipnoi and what little there is deals almost entirely with the spiral 

 valve. 



Leveschin, 70, described villi in Salamandra maculata, but in all 

 American tailed Amphibia no villi were found. About the simplest 

 condition was found in Siren lacertina, where the intestine in the 

 specimens examined was smooth. The most common form of fold was 

 a simple longitudinal rather straight or slightly wavy kind which in 

 many cases was rather thick; such folds as are found in Necturus, 

 Gyrinophilus, Amblystoma, etc. (Figs. 3 and 4). Another form of fold 

 was found in the intestine of Amphiuma. In this animal the folds 

 are quite numerous and zigzag with rather sharp angles (Fig. 2). Villi 

 have been described in very few Anura. The folds described in Euro- 



