74 HELEN DEAN KING AND HENRY H. DONALDSON 



compiled by Hatai ( '14) giving the weights of the several 

 organs in the wild strain. Taken altogether, these tables indi- 

 cate the values for the several organs in the wild strain and 

 give a basis for determining the changes shown by the captive 

 Grays. 



For conciseness we shall use, in the subsequent text, the 

 term 'captive Grays' for the Norway rats here considered. 



In forming the tables and charts that follow, the procedure 

 has been this : The datum for any organ or part of an indi- 

 vidual captive Gray is compared with the corresponding 

 datum from the appropriate reference table, the comparison 

 being based either on the observed body weight or body length. 

 Using the datum in the reference table employed as the stand- 

 ard, the percentage deviation, plus or minus, of the observed 

 values for the captive Grays has been determined. The aver- 

 age of all the individual variations in one sex group of a given 

 generation is the datum entered in the condensed tables here 

 presented. 2 



The deviations based on the observed body weight and 

 on the observed body length are both given in the tables. 

 As will be shown later, however, the body weight exhibits a 

 relative increase between G! and G JO , and for this reason only 

 the deviations based on body length are used for the graphs 

 in the charts. In tables 11 and 12 there are given for each 

 sex of each generation the average ages and the average body 

 lengths, but these data are not repeated in the later tables. 

 In the charts the reference-tables values are represented by 

 the base line and the percentage deviations of the captive 

 Grays are entered in their proper relations to this. The same 

 base line, of course, represents the reference values for both 

 males and females. Any departures from this general ar- 

 rangement of the tables or charts will be noted as they occur. 



BODY LENGTH 



The values for the mean body length as given in tables 11 

 and 12 are entered in chart 12. The fluctuations in the graphs 



' The individual data are on file at The Wistar Institute, where they may be 

 consulted. 



