METACHEMOGENESIS IN INSECTS — ROCKSTEIN 281 



valid, it would be reasonable to expect to find a counterpart of meta- 

 chemogenesis (as it has been described for a number of holome- 

 tabolous forms) in insect species with such "gradual metamorphosis." 

 At least two such studies have indicated that such a period of post- 

 emergence biochemical maturation may indeed be characteristic of 

 Hemimetabola, as well. Thus McShan and his coworkers (1954) 

 found that succinoxidase activity of the pink thoracic muscles of the 

 Madeira roach, Leucophaca maderae, increases significantly from one- 

 half hour of age to the fifth day after the final moult. This elevated 

 activity persists through the 30th day, after which there is another rise 

 in enzyme activity to a maximum at 40 days of adult life equal to 

 50 percent higher than that of the original half -hour-old adult. In a 

 later study, Kramer and McShan (personal communication, 1955) 

 found that succinoxidase activity of the basal leg-thoracic muscles 

 of the male American cockroach, Periplaneta americana (Linnaeus), 

 increased by about 60 percent from the 12-hour- to the lo-day-old 

 adult. In both species, also, they found a slow, continuous increase 

 in dry weight of thoracic muscle over the first 60 days and 10 days 

 of adult life, respectively. Brooks (1957) clarified further the age- 

 succinoxidase activity relationship in the American cockroach ; she 

 observed that the biochemical maturation of the pigmented (pink) leg 

 and wing muscles, in terms of succinoxidase activity, has its ana- 

 tomical counterpart in the degree of pigmentation of the muscles. 

 Thus, in the nymphs of both sexes, all leg and wing muscles are white 

 and the succinoxidase activity is at a minimum. In the male cock- 

 roach, the final moult is marked by a rapid increase in pigmentation, 

 accompanied by a concomitant rise in succinoxidase activity in the 

 muscles which are primarily concerned with flight. By the third week 

 of adult life, this activity has reached a (maximum) value equal to 

 about six times that of the newly emerged adult male; this high level 

 is maintained for a considerable period of time thereafter. In the 

 female cockroach, on the other hand, both pigmentation and associ- 

 ated succinoxidase activity do not change for at least 2 months after 

 adult emergence ; at this late time (when the male muscle pigmenta- 

 tion and enzyme activity have been at a maximum level for well over 

 a month), the muscles of the female show only a faint pigmentation 

 and possess a succinoxidase activity about one and one-half times that 

 of the younger females and less than one-third that of corresponding 

 muscles from males of the same age. 



Finally, as in the case of the Holometabola, endocrinological studies 

 suggest the role of the maturing corpora allata as a higher level con- 



