NOTES ON NEGLECTED PHASES IN METAMORPHOSIS, AND A RELY TO WHITTEN,JM

Growth is a continuing process but discontinuous events make it possible to consider the process in stages. Over a period of 3 decades R.E. Snodgrass reiterated the view that in arthropods a new stage begins with the detachment of the epidermis from the old cuticle, an event now known as apolysis. According to Snodgrass, ecdysis does not occur until sometime after the new stage has begun. All known facts of development support this view. The difficulties that arise when a new stage is considered to begin at ecdysis are considered at some length. For many purposes there is no reason to abandon the use of ecdyses to designate intervals of development.