264 



HISTORY OF THE HUMAN BODY 



but a few windings, the change taking place within a few 

 weeks or even days in correlation with a change of food (Fig. 

 73). Allowing for a few isolated cases, however, the canal, 

 of fishes and amphibians is short and becomes considerably 

 lengthened in the Sauropsida and Mammalia, where the in- 



FIG. 73. Comparison of alimentary canal in (A), tadpole and (B), 

 adult frog. [After the LEUCKART wall charts.] 



testine, the part mainly involved in the increase of length, 

 becomes disposed in complicated folds and windings. These, 

 although apparently wholly irregular in their disposition, may 

 be referred to a definite system, as may be made clear by a 



