61 THE AMERICAN NATURALIST [Vol. LII 



The actual curves look like the example in Table IV of 

 an F 2 cross. 



TABLE IV 

 ZA9 F 2 from MXH 



The sum of all the hundreds of curves shows that we 

 are dealing here with a case of multiple allelomorphism : 

 The pigment factor, producing the gradual covering of 

 the markings, is present in the different races in different 

 degrees, all being allelomorphic to each other. 



Thus far we have dealt only with the very young cater- 

 pillars. Their further history in regard to the effect of 

 these factors leads us one important step further. We 

 find mainly the following types of behavior within the 

 pure races: (1) Light marked caterpillars, which remain 

 practically the same throughout the entire larval life. 

 (2) Light-marked caterpillars which grow darker with 

 every moult and finally are about medium or more than 

 medium dark. (3) Light-marked caterpillars which 

 change during the larval stage, so that they finally are all 

 dark. (4) Medium light caterpillars of different degrees 

 changing to dark during larval life. In the following 

 tables we give a few examples of these races, showing the 

 shifting of the type of marking during the stages of larval 

 life. The large range of variation after the third and 

 fourth moult visible in these tables is due more to a dif- 

 ferent speed of shifting in different individuals than to 

 the initial variability. This is shown in Table VI, which 

 gives an example of the shifting of types of pigmentation 

 during the larval stages for a series of isolated individ- 

 uals of some of the pure races. 



The genetic analysis of this phenomenon seems to re- 

 veal the real nature of the multiple allelomorphs, which 

 cause these different types of pigmentation and their 

 behavior during development of the caterpillars. With- 



