1158 THE METABOLISM OF NUCLEIN AND [pt. iii 



Yet if this is what happens in the simplest alecithic eggs, there is 

 abundant evidence that it is not so in the most compHcated ones. The 

 preceding pages have demonstrated that the chick makes most of its 

 nucleoprotein itself. We know practically nothing about this aspect 

 of reptilian development, but the silkworm, as has been mentioned 

 above, resembles the chick in nuclein synthesis. When, however, we 

 pass to aquatic vertebrate eggs we find that the conditions are re- 

 versed, not because we know what occurs during development, but 

 because notable quantities of nucleoprotein are found in the un- 

 developed eggs, in agreement with those of aquatic invertebrates and 

 in contrast to terrestrial animals. Ichthulin itself, as has been de- 

 scribed in Section 1-13 almost certainly contains no purine bases, but 

 when the eggs have been worked up as a whole, investigators have 

 found them (Levene & Mandel and Mandel & Levene on cod, 

 Tschnernorutzki and Steudel & Takahashi on herring, and Konig & 

 Grossfeld on herring, carp, cod, pike, and sturgeon eggs). Henze 

 isolated over i per cent, of pentose from dried octopus eggs. Finally 

 it is likely that nematode eggs contain large stores of nucleoprotein 

 for Faure-Fremiet found a good deal of the phosphorus to be com- 

 bined in that way. We may summarise these facts in the following 

 table : 



there is nothing like enough nucleic acid (as judged in this way) in the fertilised eggs of 

 invertebrates to provide for the increase in nuclear material during development. If the 

 nucleoprotein of the egg, however, contained pentose and not hexose, it would not give 

 the Feulgen-Rossenbeck reaction and this, Brachet suggests, is the explanation of the dis- 

 crepancy. Such an explanation is particularly plausible in view of the work of Calvery 

 (seep. 1 147). 



