XI. FAMILY HISTORIES 



WE may now take up in detail the family histories. Fig. 10 gives 

 a graphic representation of matings, from which were selected two 

 mice, No. 20 Y $ and No. 26 Y $, that made the unusually poor 

 records of 115 and 183 seconds respectively, though the other mice 

 in the same litters had good records. The parentage of Nos. 20 and 

 26 was unknown ; they were mated and gave two litters, each com- 

 posed of three males and one female. Three mice in these two litters 

 gave unusually slow records and made considerably more errors than 

 normal. Two other mice gave poor records; two gave good records, 

 while one died before it was tested. It is unfortunate that both fe- 

 males in these litters died before further offspring could be obtained. 

 Table 1 gives the complete record of both time and error averages 

 for these mice. It is a question whether or not selection of parents 

 having poor records tended to produce more than the normal number 

 of offspring slow to learn. Further investigation can alone afford an 

 answer. 



The mice whose records are given in Tables II. and III. are 

 graphically represented in Figs. 11 to 14 inclusive. They have been 

 carried down to the eighth generation and are still being tested. 

 These animals are related and compose a group which is here called 

 the white family. The matings began from an original pair of albino 

 mice that were purchased from a dealer in the spring of 1913. The 

 records for the parents and the first six generations are given in Fig. 

 III., and it is to be noted that the time averages for the animals, 

 whose catalogue numbers are lower than 128, are based upon per- 

 formance only in the initial learning period in the maze test. The 

 time records for all the animals of the F 7 and F 8 generations, and 

 one family, Nos. 135 to 138 in the F 6 of Fig. 12, are based on an 

 average performance in all the tests as previously explained. 16 The 

 parents of the white family, Nos. 8 and 9, were quick to learn, mak- 

 ing averages of thirteen and eighteen seconds respectively. The first 

 generation was composed of four mice, one was not tested, two took 

 considerably longer to learn the test than either of the parents, while 

 the remaining animal made a quick record. The family average 

 equalled 59.7 P.E. 15.7 seconds. A successful mating was ob- 



"The average time for the 71 mice that was calculated upon performance 

 in all tasks was 55.& P.E. 3.5 sec., and this was practically identical with the 

 average time made by the 183 mice that was based on the records for only the 

 initial learning period of the maze test; namely, 54.1 P.E. 2.3 sec. 



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