FAT METABOLISM 



1 185 



Wet weight 



Dry weight 



Total ether extract 



Neutral fat fatty acids.., 



Phosphatide fatty acids 



Cholesterol 



Thus 20 per cent, of the initial amount of ether extract in the silkworm 

 egg disappears between the end of the diapause and the time of 

 hatching, and when the neutral fat fatty acids are alone considered 

 the fall reaches 46 per cent, of the initial value. This was later con- 

 firmed by Farkas who found a fall of 49 per cent. The only other 

 data which we possess for the silkworm are those of Vaney & Conte, 

 but it is likely that their methods were inadequate and they isolated 

 less than half the amount of total fatty acid found by Tichomirov. 

 Their figures were as follows : 17 • j • 0/ 



° Fatty acids m % 



dry weight of egg 

 4 days after laying ... ... ... ... 7-21 



6 days after laying ... ... ... ... 6-68 



End of the diapause (g months after laying) ... 5-35 



Hatching (lo months) ... ... ... ... 4-88 



and suggested a loss of 2-33 per cent, of the dry weight, or 32-3 per cent, 

 of the initial weight. Kaneko has made a histochemical study of the 

 fat in the silkworm egg, especially concerning himself with its localisa- 

 tion. Another piece of information concerning fat metabolism in 

 insect eggs is due to Weinland, who made a ^'Brei" of the eggs of 

 the blowfly, Calliphora vomitoria, and adding Witte's peptone, found 

 after some days of anaerobic action a decrease of about 30 per cent, 

 in total fatty acids. This stood in the sharpest contrast to the behaviour 

 of "Breis"" of larvae and of pupae, which have a remarkable power of 

 converting peptone and even protein into fatty acids. It would thus 

 appear that Calliphora vomitoria embryos consume a large amount of 

 fat during their development, just as do those of Bombyx mori. Then 

 for the grasshopper, Melanoplus differ entialis, we have the careful work 

 of Slifer, who found 0-352 mgm. total fatty acid at the beginning of 

 development and 0-14 mgm. at the end; each egg, therefore, lost 

 54-3 per cent, of its initial store. This fits in well with the respiratory 

 quotients of 0-7 to o-8 which, according to Bodine, are always found 

 for this material. 



