. Analysis of development. Embryology; Embryology. Metamorphosis 641 stimulating the prothoracic glands to secrete their hormone. The brain hormone corre- sponds to the factor variously designated as "molting hormone," "metamorphosis hor- mone," "pupation hormone," and "growth and differentiation ; Corpus Allatum Hormone. An agent pro- duced by the corpus allatum. When acting with prothoracic hormone it modifies the tissue response in such a way as to lead to a larval molt. This factor was formerly desig- three aspects of insect development: (1)
. Analysis of development. Embryology; Embryology. Metamorphosis 641 stimulating the prothoracic glands to secrete their hormone. The brain hormone corre- sponds to the factor variously designated as "molting hormone," "metamorphosis hor- mone," "pupation hormone," and "growth and differentiation ; Corpus Allatum Hormone. An agent pro- duced by the corpus allatum. When acting with prothoracic hormone it modifies the tissue response in such a way as to lead to a larval molt. This factor was formerly desig- three aspects of insect development: (1) the molting process as it occurs in the larva, (2) pupation or the metamorphic molt, and (3) the differentiation of adult structures from imaginal discs or other larval sources. Re- sults on the Diptera will be considered separately after the general discussion, since these results at first did not seem to fit in with results in the other insects. For reviews of various aspects of the problem published during the last ten years see Needham ('42), RMODNIUS PLATY5AMIA DIPTtRA Larval Molts Dram Pro+horacic Glanol tissues I Larval Molt Pupal Developments Bra i n Prothoracic Gland ^Tissues Imoginal Molt Brain Prothoracic Glanol ^^ Tissues Larval Molt Brain Prothoracic Gland J Tissues Pupal Development o/ia/oause cold Brain Prothoracic Gland C A X* ^?^' Tissues Imoqinal Development / Prothoracic Region) /^i ^Gojionx Tissues Larval Molt rinq Brain. Pupal & Innao|lnal Dewel Fig. 225. Schemata of endocrine relations in insect metamorphosis according to the Wigglesworth- Williams concept. nated as "inhibitory hormone" and "juvenile ; Prothoracic Gland Hormone. An agent pro- duced by certain glandular cells of the in- sect's thorax (in some extending also into the head region). It seems to act directly upon the tissues, stimulating them to assume the adult condition except when acting in con- jimction with factor as noted above. The prot
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