THE YPSILOID APPARATUS OF URODELES. 



283 



body swings upward, however, there occurs a marked constric- 

 tion of the posterior part of the abdominal cavity, often so pro- 

 nounced that the ventral wall (that is, the ypsiloid region) is 

 drawn sharply upward ( x Fig. 10, a). In this condition the ventral 

 contour of the body exhibits an angle between this posterior and 

 the more anterior region. These changes of shape may best be 



FIG. 10. Diemyctyhts ririJesctns ; (a) showing the body directed upward in 

 swimming as a result of the compression of the posterior portion of the body cavity 

 through the action of the ypsiloid apparatus; (^ showing a characteristic floating 

 position with the posterior portion of the body cavity expanded and the anterior end 

 of the body depressed. 



seen in a specimen which has not been fed for several days, since 

 they are partially masked by the presence of masses of food in 

 the digestive tract. 



They occur, moreover, not only during this inactive change in 

 the direction of the long axis of the body, but changes of direc- 



