224 PROBLEMS OF GENETICS 



represented as due to the action of three factors, any of which 

 may be independently present or absent. The stripings of the 

 elytra and of the larvae are each due to a separate factor. As 

 regards the distinction between the yellow and the white larvae 

 the evidence does not prove that there is decided dominance of 

 either colour and I infer that the heterozygotes are often inter- 

 mediate. 



The chief contribution which this new paper claims to make 

 relates to differences in the results which ensue from crosses 

 effected between these three types at different average tempera- 

 tures. 



We are first concerned with four experiments which I number 



(i), (2), (3), (4): 



i. Signaticollis 9 X diver sa o 71 bred at an average tempera- 

 ture of 8o° F. by day and 75 F. by night, gave two groups in 

 about equal numbers. The first (49) was pure signaticollis and 

 bred true. The second (53) was of an intermediate type, which 

 on being bred together gave the typical Mendelian result — 1 sig.: 

 2 intermediate: 1 div. 



2. Next, as the account originally stood in the published 

 paper, we are told that sig 9 X div d 1 bred together at a day- 

 temp, average 75 F. and night average 50 F. gave an inter- 

 mediate only, which subsequently produced a normal 1:2:1 

 ratio. The two crosses were repeated eleven times with identical 

 results. 



In a further experiment (3) signaticollis 9 X diversa d" were 

 bred under the same conditions as those used in expt. (1). They 

 again gave sig. and intermediates as before in fairly equal numbers. 

 The sig. as before bred true, and the intermediate gave 1 : 2 : 1 , 

 all exactly as in expt. (1). 



In expt. (4) the same parents used in (3) were again mated 

 under conditions of expt. (2) at the lower temperature, and this 

 time gave signaticollis exclusively, which bred true for four 

 generations. This experiment was repeated seven times with 

 uniform results. 



Diagrams are given representing all these histories in graphic 

 fashion. 



