ABSTRACT
The body cells of the developing insect carry the potentialities for both larval and imaginal differentiation. During larval life imaginai differentiation is suppressed because in the presence of the juvenile hormone (sometimes referred to as the ‘inhibitory hormone’), secreted by the corpus allatum, the intracellular system which leads to the formation of larval structures takes precedence over the system which leads to the formation of adult structures (Wigglesworth, 1940).
As pointed out elsewhere (Wigglesworth, 1952), the ‘moulting hormone’ is composite and consists of a factor secreted in the brain that activates the thoracic gland which then secretes the hormone which initiates growth and moulting.
The lethal temperature, defined here as the temperature at which 50 % of larvae 1 day after feeding are killed within 24 hr. is about 40° C.
