CRUSTACEAN METABOLISM 221 



tinct decrease in carotenoid content of the gland in all stages except late 

 C, when there was a very marked increase. This suggests that sex is a 

 factor in carotenoid metabolism, which is not surprising in view of the 

 extensive deposition of carotenoids in the eggs. 



Lenel (Lenel and Veillet, 1951; Lenel 1953a,b, 1955) has observed 

 that removal of eyestalks from Carcinns maenas in stage D results in a 

 sudden change in the color of the pigmented layer of the new integument 

 from dark to bright red, with no change in the total carotenoid content. 

 This suggests that an eyestalk factor, presumably not the molt-inhibiting 

 hormone, is concerned in the conjugation of carotenoids with protein 

 which occurs during formation of the integument. 



Tissue Metabolism and Enzymes 



The changes in oxygen consumption and the metabolism of protein, 

 carbohydrate, and lipid which we have discussed are presumably reflec- 

 tions of changes in enzymic processes occurring at the cellular level. Ulti- 

 mate explanations of the way in which hormonal factors bring about or 

 influence metabolic changes will presumably have to be made in terms of 

 the actions of hormones on cellular processes of metabolism. Little prog- 

 ress has been made in this direction. We may assume that the basic pattern 

 of tissue metabolism in crustaceans is similar to that in mammals. 

 Wherever careful studies of enzyme systems have been made, in micro- 

 organisms, in plants, in invertebrates, or in vertebrates, the same funda- 

 mental patterns of oxidative enzymes, glycolytic enzymes, and enzyme 

 sequences have been found, with only minor variations in initial substrates 

 and products and in the relative importance of alternative pathways. 

 However, very few such studies have been made with crustaceans. 



Ball and Meyerhof (1940) found succinic dehydrogenase in the heart 

 muscle of Houiarus arnericaniis, but could not demonstrate the enzyme in 

 skeletal muscle. Scheer, Schwabe, and Scheer (1952) found no evidence 

 for the operation of this enzyme, or of other oxidizing enzymes of the 

 citrate cycle, in muscle or digestive gland of Pamdirus japonicus. Ker- 

 mack, Lees, and Wood ( 1954) were likewise unable to find any utilization 

 of substrates for the citrate cycle in muscle or digestive gland of Homarus 

 vulgaris. The oxygen consumption of fragments of digestive gland of 

 Pannliriis japonicus was not inhibited by fluoride or malonate ; we did find 

 evidence of an active phenol oxidase system in this tissue (Scheer, 

 Schwabe, and Scheer, 1952). Krishnan (1954) confirms earlier results 

 demonstrating a tyrosinase in the blood of Carcinus maenas. The activity 

 of the enzyme varies in the intermolt cycle, reaching a maximum in the late 

 D stages. This variation in activity is attributed to changes in the oxida- 

 tion-reduction potential of the blood. There is also a cyanide-insensitive 



