. Analysis of development. Embryology; Embryology. HORMONE BEFORE CRITICAL A PERIOD CAPILLARY TUBE. —^ FIFTH NYMPH BECOMES 6TH-STAGE (SUPERNUMERARY) NYMPH AFTER CRITICAL PERIOD BEFORE CRITICAL PERIOD Fig. 223. The union of nymphal instars of Rhodnius by capillary tubes. A, Fifth nymph, decapitated after the critical period and thus with active glands, is coupled with a first nymph, decapitated before the critical period. Both individuals undergo imaginal molts, the first nymph becoming a diminutive adult. The fifth nymph of Rhodnius, serving as the donor in this instance, furnishes prothoracic
. Analysis of development. Embryology; Embryology. HORMONE BEFORE CRITICAL A PERIOD CAPILLARY TUBE. —^ FIFTH NYMPH BECOMES 6TH-STAGE (SUPERNUMERARY) NYMPH AFTER CRITICAL PERIOD BEFORE CRITICAL PERIOD Fig. 223. The union of nymphal instars of Rhodnius by capillary tubes. A, Fifth nymph, decapitated after the critical period and thus with active glands, is coupled with a first nymph, decapitated before the critical period. Both individuals undergo imaginal molts, the first nymph becoming a diminutive adult. The fifth nymph of Rhodnius, serving as the donor in this instance, furnishes prothoracic hormone with little or no hormone. B, Second-stage nymph, decapitated after the critical period, is combined with a fifth nymph that had been decapitated before the critical period. The second nymph, acting as the donor, delivers both and prothoracic hormones into the body of the fifth nymph. The fifth nymph molts and, under the influence of both hormones, becomes a sixth-stage (supernumerary) nymph. (From C. D. Turner, Gen- eral Endocrinology.) from the thorax of activated individuals is sufficient in itself to induce molt in non- activated abdomens. Thus the picture of the mechanism of metamorphosis in Rhodnius may be diagrammed as in Figure 225. PLATYSAMIA The work of Williams on Platysamia began with an analysis of the mechanism of diapause in this lepidopteran. The animal normally spends the winter as a pupa, and experiment has shown that the freshly col- lected pupa will not develop into an adult unless it is first exposed to a period of at least two weeks of cold. Williams ('46) was able to show that the influence of cold was exerted through activation of hormone pro- duction in the animal's brain. An activated animal induces imaginal development in a non-activated parabiont. The brain from a cold-treated animal is effective in breaking activated brain into a diapausing abdomen is not effective unless a prothoracic gland is implanted along with it. At first
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Keywords: ., bookcentury1900, bookpublisherphiladelphi, booksubjectembryology
