58 



tIz., those about to discharge in the direction for 

 progression, in the one case, or retrogression in the 

 other, which we shall term Propelleks, and those 

 iibout to discharge in the opposing direction, which 

 we shall term Bearers, since they raise the body 

 sufficiently to clear the ground. 



If the torsions by both anterior and posterior 

 points of apphcation work together so that neither 

 end of the cross-line shall (as in § 32) displace the 

 other, the spring will take place against the cross- 

 line as a centre of appui, and the result will be a 

 perpendicular locomotion, in which case there will be 

 an equal division between the bearers and propel- 

 lers in each C. 



§ 63. If the rear point of application were made 

 the leading point, the reverse of the preceding ac- 

 tion would take place, and in a snake whose struc- 

 ture allowed this mode of action, retrogression 

 would follow. In such a case the ribs discharging 

 to the fi'ont would be " hearers,'' but as this mode 

 of action will not be considered normal we confine 

 that term to ike anterior ribs in each G. 



§ 64. As to the order in which the alternating 

 ribs come to the ground, this will depend upon the 

 degree of gathering attained while " en air." The 

 propellers of the rear 0, as it were, running over 



