Modification of Germinal Constitution of Organisms 239 



pairs foimd in nature. The selected pairs were kept in separate cages, 

 as were their progeny, the only lum[)inK of material being in the statis- 

 tical treatment of it. The great majority of such pairs and their off- 

 spring were not of any mterest. Out of 311 pairs selected and mated 

 in the years 1S96-1904, only 26, or 8 j per cent of the total number of 

 pairs tried, were found capable of transmitting their particular varia- 

 tions. In many of these pairs it was certaui that only one of the 

 beetles had the character in transmissible form, so that in 311 |)airs, 

 or 622 individuals, the actual percentage of specimens showing heritable 

 variations was probably not far from 4 or 5 per cent. 



Starting from a single pair of albinic indi\'iduals in which the selected 

 character was transmissible, and following the line of descent from 

 generation to generation, the fact is graphically shown in Fig. 77 that 

 the [^articular variation of the parent was not only preserved, but 

 carried close to the limit of normal variability of the species, and that 

 by selection the race was changed from one which was variable to one 

 which was relatively invariable — that is, selection resulted in the pro- 

 duction of a race of albinic beetles of low variability, which, no doubt, 

 it would have been easy to maintain for a long period of time. From 

 the third generation a selection was made for the parents of the fourth of 

 the most and least albinic individuals, (A) still being the albinic race 

 and (B) the divergent race tending toward the opposite extreme. These 

 two lots of parents gave in the fourth generation two distinct polygons 

 which overlapped, only in the slightest extent. By continued selection 

 the polygons in the fifth generation did not overlap, and in this genera- 

 tion further division was made of (B) into (B) and (C). These two 

 lines were continued for several generations, diverging from the (A) 

 line, but not far nor ra[)idly. In the second generation there arose 

 two distinct groups separated by a wide gap (A) and (Dj, the latter 

 being the exact opposite of the (A) race. This (D) race was propa- 

 gated, and by selection produced the result shown in the polygons 

 along the line of descent (D), giving in the last generation of the race a 

 group of beetles of almost uniform condition. In all the lines of descent 

 (A), (Bj, (C), and (D), artificial selection did just what it was found to 

 do in the elements of coloration, namely, it created a race of low vari- 

 ability about the standard chosen which it maintained as long as selec- 

 tion was practiced; but it did not carry the race beyond the normal 



