124 P. S. CHEN 
analysis on A. occidentalis and A. freebornt. The former is a coastal form, while the latter 
a continental form. Several spots were identified in adults of the A. freeborni population 
but not in those of the A. occidentalis. In a mixed population, the chromatographic 
pattern was found to be quite homogenous and more similar to the neighbouring A. 
occidentalis group. 
Considering the differences in diet, living conditions and other inherent metabolic 
processes, biochemical differences between individuals of systematically far-related 
groups are expected. On the other hand, a closer examination of the general amino 
acid patterns found for the various insects referred to above discloses a high degree 
of similarity. Small variations in some cases could only be due to differences in the 
sampling and other technical procedures. Especially if specimens collected from natural 
populations are employed, there is usually no reliable information on the previous 
history of such individuals. Without careful control of the metabolic states of these 
specimens, we do not know whether the detected differences are of real taxonomic 
characters, or reflect simply individual variations. Paper chromatography is no doubt 
a useful taxonomic tool, but can be applied only under well-controlled conditions. 
FREE AMINO ACIDS AND DEVELOPMENT 
Embryonic development 
One of the outstanding biochemical properties of insects is their changes in amino 
acid patternsin the course of development. This is particularly evident in holometabolic 
type (for references see CHEN?®: 3°), During embryogenesis protein metabolism is 
especially intensive, and involves mainly the breakdown of yolk materials and their 
conversion into organ-specific proteins. The analyses of VON DER CRONE-GLOOR?? 
showed that the following free ninhydrin-reacting substances are present in the develop- 
ing egg of Drosophila melanogaster: aspartic acid, glutamic acid, glutamine, serine, 
taurine, cystine, glycine, threonine, alanine, histidine, lysine, arginine, tyrosine, 
tryptophane, y-amino-7-butyric acid, three peptides and probably proline, valine and 
leucine. Arginine, S-alanine and y-amino-7-butyric acid appeared only at the end of 
embryonic development, whereas cystine was present only at the early stage. The total 
quantities of ninhydrin-positive materials drop to a minimum shortly before hatching. 
Quantitative determinations on individual components indicate that aspartic and 
glutamic acid fall off rapidly during development, while alanine and glutamine 
show a distinct increase, particularly at later developmental period. In the egg hydrol- 
yzates of D. melanogaster and D. viridis, NAKAMURA e¢ al.1#2, 143 found that one sub- 
stance, probably cystine, is present only in the unfertilized egg. For D. viridis, up to 
the stage of germ-band formation, the contents of valine, lysine and isoleucine are 
quite constant, whereas glutamic acid, aspartic acid, serine, glycine and arginine ex- 
hibit characteristic variations (NAKAMURA et al.™*), 
For eggs of Bombyx mori, DRILHON AND BusNEL*® identified four amino acids 
(glutamic acid, serine, alanine, valine) at the time of fertilization and six amino acids 
(glutamic acid, serine, alanine, valine, tyrosine, leucine) during diapause. Glycine 
appeared later, and at the end of incubation five additional amino acids (tryptophane, 
proline, hydroxyproline, cystine, histidine) could be detected. Furthermore, the 
References p. 132/135 
