J. S. HrrxLEY 231 



The following table gives the data. All broods in which there was 

 any doubt over the eye-colour of any individual have been excluded from 

 the main table, but are given at the close for the sake of completeness. 



TABLE I. 



Red 



No-wliite Albino Colourk-ss 



Category n, C, W B,C,v> b,C,W b, C, w B {b), <; W li(h),<:,v; ToUls 



At room temperature (74 

 broods) 



First broods after trans- 

 ference from room to 

 25° C. (15 broods) 149 29 62 210 



C. Subsequent broods at 

 25° C. (41 broods) 



I). Total of A , B, and C (133 

 broods) 



1129 



642 



2011 



E. Total of (£>) with all 

 doubtful broods added 

 (13 more broods) 1293 353 563 2209 



F. Expectation for (/)) if no 848-4 282-8 •282-8 94-3 377-1 125-7 

 linkage present ' . ' ' r—-^ ^ , •' 



1131-2 377-1 502-8 •2011-1 



It will -be seen that, while Albino + Colourless are close to expecta- 

 tion, the ratio of the W to the w classes, as I mentioned above, shows 

 some peculiarities, the classes containing imu usually appearing slightly 

 in excess, especially at the higher temperature. The reason for this is 

 not yet apparent ; but whatever the cause, the deviations do not support 

 the idea of linkage of W with the other factors. 



When we come to the ratio of blacks to reds, however, we find an 

 excess of blacks and a deficiency of reds, both in the with-white and no- 

 white classes. The ratios of black to red previously obtained by Allen 

 and Sexton {loc. cit, p. 343), when only the factor-pair B, b was involved, 

 conformed very closely to the expected 3:1. Differential mortality may* 

 also for this reason be excluded. Since in my stock B came in with 0, 

 and b with c, we should expect to find this excess of blacks and deficiency 

 of reds (a con-esponding excess of reds and deficiency of blacks being 

 carried by the albino and colourless classes). 



Assuming that there is linkage between B and C, then let r be the 

 geometric mean of the linkage values p and q. We then find that the 

 value of r, as calculated from the totals in (D), is given as follows : 



2 +pq 1190 „ , . , , — ^g_. 



, -- = -r:^ irom which r — \ pa = bZoo ; 

 I — pq 303 



and 100 (1 — r) . (= mean crossover-value) = 37"45 + 0'69 7c- 



This gives a gametic ratio of almost exactly oBC : SBc : 'ibC : obc. 



