484 JOHN LINCK ULRICH 



appears to be a greater tendency of the right ipsilateral fore 

 thrust to gain an ascendancy over the left fore thrust. This 

 statement will again be considered when investigating learning 

 in the maze problem. 



When direct progression in one common path to the plane is 

 facilitated, plunging the plane must be accomplished, and this 

 last act is the most difficult to perform. It was observed, in 

 learning the latch-box problem, posturing to produce the neck 

 reflex could not readily be facilitated, and again it is noted, that 

 posturing and the production of the extensor thrust is as difficult 

 as posturing under the latch, if not more difficult. In both 

 instances posturing is dependent upon the degree of the devel- 

 opment of reflex mechanisms. There exist therefore, similar 

 difficulties which give rise in a way to similar behavior, some 

 phases of which are more pronounced in the inclined-plane 

 than in the latch-box problem. When the reflex thrusts in rats 

 are undeveloped, the repeated advances to the plane indicate 

 that posture is impossible and consequently methods to plunge 

 the plane, other than the use of the extensor thrust appear, and 

 these other methods are less efficient and even more difficult to 

 use than the extensor thrust. In the case of the latch-box 

 problem, where some form of posture is necessary to plunge the 

 plane, imperfect responses before the latch occur and only one 

 other method, the use of the teeth is employed. The repeated 

 advances to the plane without plunging it are equivalent to the 

 disruptions of directive integration in the latch-box problem; 

 the use of methods to plunge the plane other than the extensor 

 thrust is similar to the use of the teeth to raise the latch instead 

 of the neck reflex movement. These conditions arise because 

 posture is difficult to attain when the reflex mechanisms of the 

 rat are undeveloped. 



Again, as in the case of the latch-box problem, fluctuations in 

 the reflex extensor thrusts often increase the difficulty to facili- 

 tate posture, and the continued use of one method. This be- 

 havior results in the production of imperfect responses. The 

 records in tables 11 and 12 show that when only one method, 

 the extensor thrust, is used, then fluctuations in these thrusts 



