SECT. 9] PROTEIN METABOLISM 1121 



slight), but definite changes during the three weeks of active growth 

 and differentiation in the spring. The protein nitrogen decreases by 

 3-71 or 3-87 per cent, of the original value, and this loss, probably 

 all uric acid, plus the undetermined and ammonia nitrogen, almost 

 exactly makes up the 7-76 per cent, of non-protein nitrogen present 

 in the egg-contents at hatching. It is interesting to see the complete 

 disappearance of the free amino-nitrogen, a result which by no 

 means agrees with Monzini. Nor does the small loss in protein 

 nitrogen agree with the large loss found by Pigorini, but Russo's 

 figures are the later ones, and are certainly to be preferred. 



Another insect egg which has been investigated to some extent is 

 that of the lackey-moth or tent-caterpillar, Malacosoma americana. 

 Rudolfs determined the total nitrogen in it during embryonic life, 

 and reported simply that it rose from 11-5 per cent, of the dry weight 

 to 14-4 per cent, at hatching. As this figure was for the whole egg- 

 masses, including the cases, it can be only an apparent rise, due to 

 the diminution of something else, and, as Rudolfs did not publish 

 his data for absolute weights, his results are dilBcult to interpret. The 

 fat is known to diminish in this egg, and consequently the nitrogen/fat 

 ratio rises during embryonic life. Rudolfs also gave one analysis of 

 the egg-contents and egg-case separately towards the end of develop- 

 ment, but there is nothing to compare it with. Free amino-nitrogen, 

 free ammonia, urea, tryptophane, tyrosine, etc., were all tested for 

 and found to be present. The presence of free ammonia (3-54 mgm. 

 per cent.) in the egg-case and of free amino-acids (0-83 mgm. per 

 cent.) suggested to him that these were decomposing, and furnishing 

 amino-acids to the eggs inside. Such a process had previously been 

 thought to take place in the silkworm egg. 



We know nothing about the nitrogen metabolism of nematode 

 eggs, except that Kozmina found as much nitrogen present at the 

 end of Ascaris development as at the beginning. 



Our knowledge of the protein metabolism of the echinoderm egg 

 is also in a very backward state, but Ephrussi & Rapkine have done a 

 good deal to fill the gap. Working on the eggs of Strongylocentrotus lividus, 

 they found the following figures : 



% of the dry weight 



