BLUE-GREEN CATERPILLARS 409 



SUMMARY 



1. Numerous (ca. 44) conspicuous blue-green caterpillars 

 appeared in August, 1920, in closely inbred stock of the protec- 

 tively colored grass-green caterpillars of Colias philodice. 



2. The three broods in which they first appeared clearly showed 

 the 3:1 ratio, grass-green (i.e., yellow-green) being dominant, 

 blue-green, recessive. Hence their six parents were all heterozy- 

 gous (grass-green) dominants. Five of the latter were brothers 

 and sisters, one a cousin, derived from two pairs of grandparents. 



3. The matings of each of these two pairs of grandparents 

 must have been of the type: normal (dominant) grass-green 

 X heterozygous grass-green. All four had been hibernating 

 caterpillars, the offspring of a wild female (with white wing color) 

 of the fall brood of 1919. She, or her mate, was probably also 

 a heterozygous grass-green caterpillar, the other member of 

 the pair being normal. The mutation is thus to be traced back 

 to one of the individuals of this pair. 



4. This is an example of recessive mendelian factors, (mutations) 

 existing unsuspected in true-breeding wild stock, but brought to 

 light by inbreeding. 



5. In the second generation, the offspring of two recessives, 

 blue-green X blue-green, bred true. A pair of grass-green 

 heterozygotes gave an excess of recessives, but the total 

 numbers were very small. 



6. The mutation is not sex-limited. 



7. Two non-inherited pigments derived from the chlorophyl 

 of the food plant, and probably only slightly modified by diges- 

 tion and combination with other proteids (Poulton, '85), are 

 the physical basis of the dominant and recessive colors. They 

 are xanthophyl, a yellow pigment, and chlorophyl a, of blue- 

 green color. Both probably exist together in normal grass- 

 green hemolymph. 



8. The hereditary nuclear enzyme, or recessive gene, in- 

 volved in this case is a decolorizer (inhibitor) of xantho- 

 phyl. Since it is recessive, it must be present in double dose 

 (homozygous condition) in order to produce its effect. It 



