750 THE AMERICAN NATURALIST [Vol. XLV 



ceeded at once. Other beetles were kept in the air as a 

 cheek upon the results, and in some instances one elytron 

 was removed, and either the beetle minus one elytron 

 was placed in the carbon dioxide and the other elytron 

 kept in the air as a check, or vice versa. The same results 

 were obtained when pure hydrogen was used instead of 

 carbon dioxide. I found that it was impossible to obtain 

 entire absence of oxygen when either rubber or cork 

 stoppers were employed, for on long standing some 

 traces of oxygen, apparently, diffuse through the rubber 

 or cork, and cause pigmentation to proceed. 



If a beetle with unpigmented elytra be kept submerged 

 in water by means of a small weight, for example in a 

 test tube under a ten cent piece, no coloration appears 

 in thirty-six hours, while in a check the pigmentation 

 was complete in twelve hours. When, however, the 

 beetles were removed from the water and exposed to the 

 air, pigmentation proceeded at once. In most cases the 

 beetles revived after having been submerged for thirty- 

 six hours, as did those that had been forty-eight hours in 

 carbon dioxide. Heating an unpigmented elytron at 70° 

 for one minute totally inhibits pigment formation. The 

 above results are identical in every respect with those 

 which I have reported in the case of the periodical cicada 

 (1911) and the meal worm (1910 b.), so that there can be 

 no doubt that the formation of the pigment in the elytra 

 of the Colorado potato beetle is an oxidation. Tower 

 states (1903, p. 53) that the cockroach, Phyllodromia 

 germanica Linn, was used in contributing to his conclu- 

 sions, and Phisilax (1905) has since shown that in this 

 material the pigmentation is due to an oxidation induced 



Evidences of Enzyme Action—Tower claims to have 

 shown the presence of enzymes by finding stained 

 zymogen granules in some of his sectional material. He 

 states (1903, p. 60), "it was impossible to prove the ex- 

 istence of a zymogen in the hypodermis of much of my 



