218 INVERTEBRATE PHYSIOLOGY 



and the absolute amount of this substance in the blood, increase steadly 

 from C2 until the molt, and then fall off very sharply. The glucosamine 

 content of the hypodermis increases during the same period, but less 

 sharply, while the glucosamine content of the digestive gland varies in- 

 versely with that of the hypodermis, reaching its maximum in stage C3. 

 These changes are considered to be consistent with the transformation of 

 glycogen through glucose and glucosamine to chitin. Malaczynska-Suchcitz 

 (1949) and Travis (1955), using histochemical methods, confirmed these 

 observations qualitatively with respect to glycogen, and concluded that 

 glycogen is the precursor of chitin. 



This view was also supported by the work of Scheer and Scheer ( 1951) 

 with Panulirus japonicus and P. penicillatus. Glucose labelled with radio- 

 active carbon was administered to these lobsters by intrapericardial in- 

 jection, and the tissues were analyzed svibsequently for radioactivity. In 

 experiments lasting up to 18 hours, the bulk of the radioactivity was recov- 

 ered in the water- and alcohol-soluble fractions of the tissues. Relatively 

 high counts were, however, found in the alcohol precipitate from depro- 

 teinized extracts of digestive gland, which would contain the glycogen, 

 and, after 18 hours, a substantial part of the radioactivity was found in 

 the chitin of the integument. 



A more startling result of this experiment was the observation that 

 little or none of the radioactivity could be recovered in the respiratory 

 carbon dioxide, even after 18 hours. This is conclusive evidence that glu- 

 cose is not used primarily as a substrate for oxidative metabolism. Further 

 evidence is provided by the observation that glucose has no stimulating 

 effect on the oxygen consumption of surviving fragments of digestive 

 gland or muscle of Panulirus japonicus (Scheer and Scheer, 1951) or 

 muscle of Hemigrapsus nudus (Hu, unpublished). Moreover, glucose is 

 apparently not removed from solution by these tissues. Further support- 

 ing evidence comes from the observation that, in 23 days of fasting, 

 Hemigrapsus nudus shows no change in glycogen content (Neiland and 

 Scheer, 1953). We may therefore conclude that the primary role of glu- 

 cose in decapod metabolism is in the formation of chitin, with glycogen as 

 a reserve or intermediate. We should note, however, the curious results of 

 Krishnan (1954) ; he finds a definite stimulation of oxygen consumption 

 by glucose and fructose in muscle extracts from Carcinus maenas in the 

 presence of large concentrations of potassium cyanide. 



Recent results of Hu (unpublished) from this laboratory indicate that 

 glucose metabolism in Hemigrapsus nudus may differ significantly from 

 that reported for Panulirus. Radioactive glucose was injected into C 

 stage Hemigrapsus, and the redioctivity recovered from the respiratory 

 CO2, glycogen, and a new polysaccharide containing glucose, galactose, 



