SECT. 4] HEAT-PRODUCTION OF THE EMBRYO 691 



It is evident that with one or two exceptions the intensity of re- 

 spiratory exchange is much greater in the egg than in the pupa, so 

 that this at any rate marks a definite difference between embryonic 

 development and metamorphosis. The respiratory quotients were 

 always found to be low. Thus Anasa tristis (the squash bug) gave 

 an initial value of 0-521 rising on the third day to 0-732, and main- 

 taining itself at that level through subsequent development, while 

 the respiratory quotient oi Leptinotarsa ranged daily from 0-512 to 

 0-68. Cotinis nitida went even lower, seldom rising above 0-524, and 

 even dropping for several days to 0-413. Popilliajaponica began with 

 a respiratory quotient of about that level, but rose in the last few 

 days of development to 0-732. No explanation is available for these 

 curious quotients; evidently either an abnormally small amount of 

 carbon dioxide was escaping or an abnormally large amount of 

 oxygen was being taken in. There seems no reason, from a technical 

 point of view, to doubt the accuracy of Fink's analyses, so it is 

 probable that in these insects whatever combustion processes are 

 going on are obscured by transformations of another order, such as 

 the passage of fat into carbohydrate. This increase of highly oxy- 

 genated material at the expense of less oxygenated material leads, 

 in the well-known case of the hibernating marmot, to very low 

 respiratory quotients, and might perhaps be due in the case of these 

 beetles to the formation of chitin. 



Melvin later estimated the oxygen uptake during the embryonic 

 development of a number of insects, using the Krogh micromano- 

 meter. The organisms employed were Anasa tristis, the squash bug; 

 Tropoea luna, the luna moth; Samia cecropia, another moth; and 

 Pyrausta ainsleii, the smartweed borer. By a method not stated, 

 Melvin was able to measure the weight of the shells of the eggs and 



