36 GARDNER CHENEY BASSET 



In Plate VIII is shown the curve of learning (below) and of 

 relearning (above) of the inbred rats compared with those of the 

 normal control. These curves are constructed from figures 

 given in Table V. The curve of the inbred rats is indicated 

 by the solid line, that of the normal control by the broken 

 line. The ordinates give the average daily time in seconds 

 for each group, and the abscissae the number of the day in which 

 such time was made. As in the other learning curves, the 

 time required by both inbred and control rats for the first 

 four days was so long that it is represented here by figures and 

 does not appear in the curve. The descent in time of both 

 inbred and control rats for the first ten days is quite rapid, 

 although both show retardation on the sixth day. From the 

 forty-first day the curve of the controls lies entirely below the 

 four second mark. The inbred curve, throughout, shows great 

 irregularities, especially on the thirtieth day, when it rises to an 

 average of nearly twenty-eight seconds. The inbred curve of 

 relearning is very similar to that of the control, and from the 

 twenty-third day coincides with it. But again, in relearning, we 

 are dealing with selected groups, the eleven inbreds and two 

 controls that failed to learn not being included. The inbreds of 

 this selected group had all releamed at the end of the twenty- 

 fourth day; the control at the end of the seventeenth day. 



In Plate IX may be seen the distribution curves of learning of 

 both the inbred and control series for the inclined plane experi- 

 ment. The time is given in days — in groups of five for learning, 

 singly for relearning. It is very apparent that the advantage 

 lies wholly in favor of the normal control series. 



Of the inbred rats used in the inchned plane experiment, 

 fifteen were from the seventh generation, fourteen from the 

 eighth, and one from the ninth- In Table VI is presented a 

 comparative summary consisting of the daily averages of the 

 seventh and eighth generation rats used in the inclined plane 

 experiment. With the rats of the eighth generation may be 

 included the one from the ninth, as her record was not far from 

 the average of the eighth. The table shows that four of the 

 seventh generation and seven of the eighth generation failed to 

 learn the inclined plane. The seventh generation required, on 

 the average, 59.60-}- days to learn; the eighth generation, 

 86.53 -t- days. The absolute retention of the seventh genera- 



