BLUE-GREEN CATERPILLARS 403 



Brood 6, which consisted altogether when brought into the 

 laboratory of sixty-nine grass-green and twenty-five blue-green 

 caterpillars, came from three successive layings outdoors, of 

 which nos. 1 and 3 were continually covered with cages, while 

 no. 2 on a spot close to the others was left uncovered from August 

 4th to 16th, owing to a lack of cages and because when setting 

 the culture I had no great interest in it (the brood being expected 

 to be homozygous for the common yellow-wing form). On 

 x4.ugust 16th blue-green caterpillars were discovered greatly 

 to my surprise in cages nos. 1 and 3. Between a third and a 

 quarter of the caterpillars in these cages were blue-green. On 

 the spot where cage no. 2 had stood during the laying of the 

 second lot of eggs, and which for twelve days had been uncovered 

 and open to the attacks of birds, almost exclusively grass-green 

 caterpillars in various stages of development were found. By 

 careful searching I succeeded in finding two very small and not 

 yet conspicuous blue-green larvae that had escaped the eyes 

 of the sparrows. It was perfectly evident that the birds had 

 found the blue-green mutants an easy mark and that, while 

 leaving plenty of grass-green caterpillars untouched, they had 

 eliminated from that part of the culture nearly every blue-green 

 individual. 



INHERITANCE OF THE MUTATION 



The evidence that the blue-green mutation is inherited as a 

 mendelian recessive is not extensive, yet definite and satisfactory 

 as far as it goes. 



As explained above in the section describing the origin of 

 the mutation, the first three broods in which it appeared were 

 from parents all of which were grass-green heterozygous domi- 

 nants. These broods are shown in detail in the following table. 



Inspection of table 1 shows that in the first generation the 

 3:1 ratio between grass-green and blue-green larvae was closely 

 approached in the total number of individuals that came through 

 to the imago, and that, in the census of all the larvae, both living 

 and dead by disease, in each of the three families, the same 

 proportion is evident. It will also be seen that the numbers 



