BLUE-GREEN CATERPILLARS • 389 



Pieris rapae, however, a somewhat closely allied form, Geyer 

 found the hemolymph of the male caterpillar to be light yellow, 

 that of the female, bright green. 



The blue-green caterpillars had been under observation only 

 about three months when this paper was written, but the 

 facts regarding the origin of the mutation, the ecological data 

 already obtained, the many-sided relations of the blood pigments 

 and the action upon them of the mutant gene, are so striking 

 and interesting that it seems best to put the case on record as it 

 stood at the close of the first season. I hope later to present 

 a more complete account of the matter, following out some of 

 the many lines of research that are hardly more than pointed 

 out in the present paper. 



I wish to acknowledge my deep indebtedness to Prof. A. Ames, 

 to whose skill the exceedingly accurate record of colors upon 

 the plate is in large measure due; to Prof. Leland Griggs and Mr. 

 Kenneth Robes for the photographs themselves; to Mr. A. B. 

 Gahan, of the National Museum, who identified the hymenop- 

 terous parasites that attacked the blue caterpillars; to Mr. 

 Rolf C. Syvertsen, who assisted me in rearing the caterpillars 

 and protecting them against disease, and to Mr. C. J. Lyon for 

 assisting me in acquainting myself somewhat with the chemistry 

 of chlorophyl. 



I extend my most appreciative thanks to the authorities of 

 The Wistar Institute for providing a plate in colors. Funds 

 necessary for the prosecution of this research were generously 

 furnished first by the President and Treasurer of Dartmouth 

 College, and later by the Carnegie Institution of Washington 

 through the kindness of Dr. A. G. Mayor, to all of whom I make 

 grateful acknowledgment. 



ORIGIN OF THE MUTATION 



The fact that the blue-green, caterpillars first appeared in 

 rather large numbers (25 in one family, 0, 18 in another, ^, text fig. 1) 

 in the same generation of inbred stock, and comprised in each 

 case approximately 25 per cent of their respective families or 



