histological change imaginal disk development IDOMAL:0002205 IDOMAL:0002205 The rudiments of some imaginal disks are present in newly hatched larvae and develop slowly during the larval stage; others appear as late as the 3rd instar. Each imaginal disk is first apparent as a plate of columnar epidermal cells which grows slowly with cell division. Increase in size of the imaginal disks occurs principally during the 4th instar, accompanied by numerous mitoses, and in most cases the disks are shaped only very approximately like the adult appendages at the time. idomal_namespace