222 INVERTEBRATE PHYSIOLOGY 



system in muscle which takes up oxygen in the presence of fructose or 

 glucose. This system is most active in the C stages, and least active imme- 

 diately before molting. The activity of the system appears to decrease in 

 captivity, and this decrease is accelerated by eyestalk removal. The avail- 

 able evidence, then, suggests that the oxidative metabolism of crustacean 

 tissues may deviate from the usual pattern. There is clear need for a care- 

 ful investigation of the problem with modern biochemical techniques. 



The first studies of the effects of hormonal factors on tissue oxidations 

 in vitro were those of Kuntz ( 1946, 1947, 1948) , which have unfortunately 

 been published only in abstract form. She first reported (1946) that the 

 dehyrogenase activity of tissue extracts is increased by addition of eyestalk 

 or sinus-gland extracts. We were able to confirm this in experiments with 

 Carcinus maenas and Panuliriis japonicus. However, the facts (1) that 

 eyestalk removal does not alter the dehydrogenase activity of lobster 

 tissues, and (2) that eyestalk extracts will increase oxygen consumption 

 of tissue homogenates, but not of surviving tissue fragments, led us to 

 doubt the significance of this observation. No consistent variation in tissue 

 respiration with the intermolt cycle could be established in P. japonicus, 

 and the only effect of eyestalk removal was that of decreasing oxygen con- 

 sumption of tissues from males to the lower levels normally characteristic 

 of females (Scheer, Schwabe, and Scheer 1952). Kuntz (1947, 1948) has 

 also reported a stimulating effect of sinus-gland extract on the phosphory- 

 lation of arginine by tissue extracts ; this work has not been repeated or 

 extended. 



From these very scanty and unsatisfactory results, two possible alter- 

 natives emerge : ( 1 ) The well-known effect of eyestalk principles on 

 oxygen consumption may not be a direct effect on tissue metabolism, but 

 rather an effect on motor activity, which in turn alters oxygen consump- 

 tion. (2) The effect may actually be exerted on tissue metabolism, but 

 more refined techniques are required to demonstrate this. 



Conclusions 



It appears from this brief survey that the best-established eff'ect of hor- 

 mones on metabolism in crustaceans is the effect of an eyestalk principle 

 on the conversion of glucose to chitin. The intermediate steps in this con- 

 version are not known ; presumably glucose is aminated to form gluco- 

 samine, the amino sugar is acetylated, and the acetylglucosamine is then 

 polymerized to form chitin. The recent discovery of the compound uridine- 

 diphosphate-acetylglucosamine suggests the possibility that this compound 

 is an intermediate in chitin synthesis. If the sequence of reactions could be 

 established, the way would be open for a test of the action of eyestalk prin- 

 ciples or of fractions isolated from eyestalk extracts on individual reac- 



