204 



O. C. Glaser 



In movements conforming to type /, Fig. i, A, the two arms i 

 and J are used as a pair, whose strong backward stroke drives the 

 animal in the direction indicated by the arrow. Arm 2, which 

 projects forward rather stiffly, serves only the function of guiding, 

 this being also the effect of ^ and 5, which are dragged behind. 

 A slight modification of type /, A, is found in type /, J5, in which 

 the distal end of arm 2 waves from side to side, and in this manner 

 adds to the propelling force furnished by / and j. Type /, C, is a 

 further modification of /, A, in which arm 2 instead of bending 

 only distally makes a stroke as effective as either that of / or j, 

 and bends either to the right or to the left, so that the animal is 



Fig. I 



propelled by two arms on one side and one on the other. The 

 course is zigzag if regular alternations in the direction of the stroke 

 of arm 2 occur but if this always falls on the same side the course 

 is circular. 



The movements that fall within this type are variable to an 

 extent which has not been pointed out. /, A^ represents in its 

 pure forms one of the two types which all previous writers have 

 noticed, though Grave ('00) has also observed the modification B, 

 of which C is the extreme case. Von Uexkiill ('05), who calls this 

 type of movement Typus Unpaar voran, says: "Beim Bewe- 

 gungstypus Unpaar voran, zeigt sich welch grosse Unterschied 

 in der Bewegungsamplitude des ersten und zweiten Gangpaares 

 besteht. Letzteres verhalt sich beinahe passiv. Doch kann es gele- 



