In last instar larvae of Galleria mellonella, the observed increase in the number of cells of growing intact imaginal wing disks was completely blocked by ligation of the mesothorax and stimulated again by external applications of low and high doses (2.6 to 130 Kglg) of ecdysterone. However, at no hormonal dose applied has the full extent of normal wing growth been attained. The ecdysteroid dependent cuticle synthesis could be induced in disks of various sizes. The cell number of imaginal disks of young last or supernumerary instar larvae is exponentially correlated with the body weight. The rates of cell division during prepupal development of the wing disk appeared to be about the same in last and supernumerary instar larvae.In normal pupae the borders of the everted wings are fitted precisely to a cuticular demarcation line on the underlying abdomen. X-ray irradiations of last instar larvae led to a reduction of the pupal wing surface and cell number, but did not affect the position of the demarcation line. The X-ray experiments confirm the finding that reduced wings are capable of normal pupal cuticle synthesis.

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