266 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I37 



Snodgrass himself has stated (1956) that "a 'legless' fly maggot has 

 legs (of the adult) developing in pouches of the skin covered by the 

 cuticle," just as the wings of a grasshopper nymph are developing 

 externally. Snodgrass also suggested (1954) that, rather than con- 

 sider "metamorphosis" the transformation of the larva into an adult, 

 the true metamorphosis in the life history is that "which has trans- 

 formed the young butterfly into a caterpillar." This he considers a 

 recent acquisition independently arisen among different orders of 

 insects (and, therefore, with no phyletic signiflcance), completely 

 dissimilar from the primitive metamorphosis of other closely related 

 invertebrates like annelids and crustaceans. 



Nevertheless, many contemporary entomologists still consider meta- 

 morphosis in holometabolous insects as the transformation from the 

 larval to the imaginal stage through the interposition of an additional 

 stage, the pupa. The variety of evidence presented in this paper serves 

 to support the concept of Poyarkoff of the pupa as a subdivision of 

 the imaginal stage, by showing the continuity of the pupal and im- 

 aginal stages in the form of postpupal maturation in the adult, 

 especially of biochemical functions. 



BIOCHEMICAL EVIDENCE FOR POSTEMERGENCE MATURATION 

 OF FLIGHT ABILITY 



In a study of the relationship between cell number and cholinesterase 

 activity in the brain of the adult worker honey bee. Apis mellifera 

 Linnaeus, from emergence to old age, Rockstein (1950) found that 

 the enzyme activity in the whole brain increased by about 15 percent 

 during the first week to 10 days of adult life; this level of activity 

 remained undiminished throughout the remainder of the bee's life. 

 (This was especially significant because the number of brain cells 

 actually fell rapidly during the first 2 weeks of life and then more 

 slowly thereafter throughout adult life; see figs, i and 2). The fact 

 that the adult worker bee does not normally make its flights into the 

 field until some time after the first week of life suggested a possible 

 relationship between the parallel biochemical changes and the develop- 

 ing function of flight during this period. Dr. A. G. Richards (1948, 

 personal communication) suggested that the decline in cell content 

 during a time when the enzyme activity was rising, implied a con- 

 tinuing neural maturation extending into the imaginal stage, which 

 includes a biochemical phase as well as the continuation of the loss 

 of larval neurones (into adult life) which was initiated in the pupa. 

 Babers and Pratt (1950), in an attempt to explain conflicting reports 



