NUTRITION AND METABOLISM 



77 



metamorphosis naturally vary in different groups, with the different 

 types of morphological change. As a rule, the large stores of glyco- 

 gen accumulated towards the end of larval life (these may exceed 33 

 per cent of the dry weight of the body in the six-day-old bee larva) 

 fall steadily, almost reaching zero in the developed adult. The fat 

 decreases rapidly at first, then more slowly (during the period of de- 

 pressed oxygen consumption) and then rapidly again before emer- 

 gence. Fat does not usually fall so low as glycogen, but only a small 

 percentage of the original store persists in the adult. In the pupa of 

 the Muscid Lucilia, it appears to be the unsaturated fatty acids which 

 are consumed, the saturated acids remaining more or less unchanged. 

 The protein is sometimes largely used in the formation of the cocoon 

 (the silkworm uses half its body protein for this purpose) ; the re- 

 mainder is extensively broken down during the early part of pupal 

 life, the non-protein nitrogen, particularly the amino acids, in- 

 creasing. With the growth of the new tissues, the process is reversed, 



fig. 11. — Ordinates: rate of oxygen uptake; abscissae: time 



A, oxygen uptake during the whole pupal stage of 9i days in Galleria, Lep. (after 

 Taylor and Steinbach); B, oxygen uptake in grasshopper, Melanoplus. During the 7 

 minutes that the curve coincides with the base line, the insect was submerged in water 

 (after Bodine) 



and the amino acids fall (p. 32). The inorganic phosphate follows the 

 same course as the amino-acids. 



These changes, and the corresponding changes in other consti- 

 tuents and in the respiratory quotient, represent, of course, only the 

 summation of the processes of synthesis and breakdown that must 



