CRUSTACEAN METABOLISM 223 



tions in the sequence. Such a test would be the sort of thing I had in mind 

 seven years ago when I started this work. Recent studies by Hu (unpub- 

 Hshed) indicate that there are no uridine-diphosphate compounds in the 

 crab Hemigrapsus nudus in stage C ; there is, however, no evidence that 

 chitin synthesis is occurring during this stage. 



In the meantime, I have developed a great interest in the whole 

 problem of crustacean metabolism and its relation to the life of these ani- 

 mals. Fascinating problems have emerged concerning the relation of 

 tissue growth to the molt cycle, the regulation of nitrogen metabolism and 

 growth, the use of stored materials as energy sources in fasting and in 

 tissue formation in the intermolt cycle, the question of sex differences in 

 metabolism, the nature of tissue oxidations, and many others. 



In closing, I should like to mention just two of these problems. Through 

 all of our work, whenever we have distinguished between the sexes, we 

 have found quantitative differences in metabolism — in tissue oxidations, 

 carbohydrate metabolism, protein metabolism, and metabolism of lipids — 

 between the sexes. Moreover, these aspects of metabolism were usually 

 influenced dift'erently by eyestalk extirpation, most often in such a way 

 that sexual differences were eliminated by the operation. There is evidence 

 that eyestalk principles are concerned in sexual matters, and it would be 

 most interesting to learn more of the metabolic actions of the sex hormones 

 of crustaceans. 



Second, the intermolt cycle involves complex and interrelated physio- 

 logical events ; the life of a crustacean is not simply a matter of molts 

 separated by long intermolt periods, but each molt is followed by a se- 

 quence of profound changes in all aspects of metabolism leading to the 

 next molt. The molt-inhibiting hormone, for the existence of which there 

 is now abundant evidence, is only one of many crustacean hormones. Car- 

 lisle and Dohrn (1953) have demonstrated a molt-accelerating hormone 

 in the prawn Lysiuafa scticandata, and we have recently provided evidence 

 that the chromatophorotrophic hormones of Leander scrratiis, some five 

 or six in number, are specifically involved in individual stages of the inter- 

 molt cycle ( Scheer and Scheer, 1954a) . It is reasonable to conclude, there- 

 fore, that many of the metabolic events concerned in the intermolt cycle 

 are under hormonal control, and that the orderly progression of the animal 

 through the cycle results from a complex sequential action of numerous 

 endocrine factors. The unravelling of some of these actions should prove a 

 most fascinating and enlightening task. 



Summary 



The oxygen consumption of crustaceans is not different from that of 

 other poikilotherms of comparable size. The rate of oxygen consumption 



