SECT. 8] CARBOHYDRATE METABOLISM 1047 



going to other forms of carbohydrate. This is one of the ways in which 

 hurried conclusions from merely histochemical evidence may lead to 

 confusion. It also shows again that glycogen cannot be considered 

 as representative of the carbohydrate group. 



One point which has resulted from these investigations of the 

 carbohydrate metabolism of the frog embryo is that there is no 

 glycogen in the liver until a very late date, so that Aron's views on 

 the assumption of its function are strongly supported. Another point 

 of interest is the probabiHty that the hatched tadpoles derive nourish- 

 ment from the jellies around their eggs. We have already seen that 

 there is some evidence that they do (p. 909). If this is the case, the 

 stores of carbohydrate in the form of mucoprotein there may be an 

 important source for the sugar of their bodies, especially as they can 

 absorb substances through their skins. It is clear that the question 

 of amphibian carbohydrate metabolism has so far only been touched 

 on, and that there is much room for an extended investigation of it, 

 including the determination of glycogen and free glucose by im- 

 proved methods on each day before and after hatching as well as 

 on parts of the animal. 



8-1 1. Carbohydrate Metabolism of Invertebrate Eggs 



A certain amount of work has been done on the carbohydrate 

 metabolism of the eggs of the nematode worm Ascaris. Brammertz and 

 Marcus, using purely histochemical methods, observed a diminution 

 of the glycogen in the eggs following fertilisation. Then Faure- 

 Fremiet estimated the glycogen before and after segmentation by 

 the Pfliiger method, obtaining 1-75 per cent, dry weight before and 

 1-05 per cent, dry weight afterwards, i.e. a loss of 0-7 per cent, over 

 the whole period. On the other hand, he obtained a figure of no 

 less than 2 1 per cent, dry weight for the ripe ovary, most of which 

 must have been in the eggs. Von Kemnitz reported histochemical 

 observations which showed that, in the ovaries before the eggs were 

 laid, they possessed large stores of glycogen. Immediately after 

 fertilisation, however, Faure-Fremiet found only 4-67 per cent, of 

 glycogen, though the chitin of the newly formed membranes ac- 

 counted for an additional 9-23 per cent. The two added together did 

 not equal the glycogen-content of the ripe ovarial eggs, from 7 to 

 9 per cent, being missing. "This quantity", said Faure-Fremiet, 

 "has disappeared without leaving any traces, and as we know that 



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