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The morphology of the developing pretarsus of Tricholioproctia impatiens was observed throughout pharate development. The imaginal discs were fully everted at 40-42 h, as timed from the white prepupal stage (0 h) and pupal-adult apolysis occurred at 52-56 h. The tissues then differentiated to form the pretarsus; the definitive size and shape of the pulvilli and claws being attained by 144 h. Volumes of the dorsal polytene nuclei increased with the develo ment of theadult pulvillus, reached an asymptoteat 144 h and remained constant during the secretion orthe dorsal cuticle. Nuclear volumes of the polytene cells declined dramatically towards the end of pharate development. In all cases the volumes of nuclei from the outside of the pulvillus were significantly larger than those of the inner nuclei. The growth and differentiation of the three thoracic pretarsi proceeded at different rates and it was shown that at most times nuclear volumes from pro-and mesothoracic pulvilli were significantly different to the volume of nuclei from metathoracic pulvilli. The implications of these findings in relation to cytochemical studies utilizing the large dorsal polytene nuclei are discussed.

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