H. (Xnsu)W 239 



(f) Hybrid {lutea x gross.) x A. grossularintd. 



A few |)iiinn^ only of this ty|H« of mating won* iimdr, and the fonr 

 faniilio8 rt^sulting an* shown in Fi^. 14. With the exception of family 

 *17 W the hyhrici jwrents wen* all a vrry |Mih' yellow, and the result, a.s 

 might l>e exjXH^tAni, is a typical frecpieney distrihution. Th«' hybrid 

 parent of *17 \V hacl a high colonr-value [24 : 22]. The oflfspring are 

 much nion» nnmerons than is represented in P^'ig. 25. There were indeed 

 82 insivts, but 64. which had a colour-value between [07 : 0*.')] and 

 [0't):0'4] and which showed no other variations of interest, were set free 

 as stxm as they emerged. The insects of family '17 W which were 

 entered in the curve (Fig. 25) may be found by reference to Table I. 

 The mther deep colour of the J parent does not seem to have hml any 

 visible effect on the colour of the oflfspring. 



VIII. Summary. 



The yellow ground colour of Abraxas grossulariata var. lutea 

 (Cockerell) is incompletely dominant over the white ground of the type. 

 It was found impossible to divide the F^ and F.y generations into distinct 

 classes, because the colours of the insects form a continuous series 

 varying from white, through the palest yellows, to a deep orange. 



A commercial instrument for the measurement of colours on an 

 arbitrary standard scale of colour-units, called the " Tintometer," is 

 described. By its means the colours of the insects have been given 

 numerical values, thus enabling the complete data of the breeding ex- 

 periments to be expressed in the form of curves showing the distribution 

 of the colour- values. When these curves are converted into percentage 

 frequency distributions, the F^ generation resembles an ordinary chanc(^ 

 di.stribution. But on the other hand the Fo generation, etc. are at once 

 seen to give curves having more than one maximum caused by the 

 tendency of the colour factors to segregate according to the ordinary 

 Mendelian laws. 



Only some of the DR individuals are distinguishable from the 1)D, 

 on account of a faint tinge of yellow in their wings. The difference 

 between the two classes, when expressed in colour-units, is not sutiicient 

 to enable the maxima representing them to be separated on the curves. 



The eflfects of sex and of variations of colour in different parts of the 

 same insect upon the measurements are considered, and the various 

 sources of experimental and statistical error are discussed. The gap on 



