. Analysis of development. Embryology; Embryology. 640 Metamorphosis. Fig. 224. Parabiotic union in moth pupae. A,B, Brainless pupa of Platysamia cecropia grafted to a chilled pupa of the same species. The brain of the chilled parabiont provides hormone necessary for the development of both animals. C,D, Brainless diapausing pupa of Telea polyphemus grafted to a chilled pupa of P. cecropia. The successful development of both pupae shows that the brain factor is not species specific. This fact also shown by E, which is adult of P. cecropia developed from a brainless pupa which had received the
. Analysis of development. Embryology; Embryology. 640 Metamorphosis. Fig. 224. Parabiotic union in moth pupae. A,B, Brainless pupa of Platysamia cecropia grafted to a chilled pupa of the same species. The brain of the chilled parabiont provides hormone necessary for the development of both animals. C,D, Brainless diapausing pupa of Telea polyphemus grafted to a chilled pupa of P. cecropia. The successful development of both pupae shows that the brain factor is not species specific. This fact also shown by E, which is adult of P. cecropia developed from a brainless pupa which had received the brain from a chilled pupa of T. polyphemus. (From C. D. Turner, General Endo- crinology.) results from a cessation of brain activity in the pupa and the consequent necessity of reactivation of the brain by exposure to cold. INSECTS IN GENERAL We may now consider whether the endo- crine mechanism discussed above for Rhod- nius and Platysamia is applicable to insects in general. Before doing so, however, a note on terminology is necessary. As experiment- ers have uncovered various factors in insect metamorphosis, names descriptive of their actions have usually been given to these factors. Such names are generally rather unsatisfactory, often being vague, too gen- eral, too restricted or sometimes even imply- ing a mode of action later found incorrect. When the source of a factor has been traced to a particular organ it is generally more satisfactory to name it in terms of that organ, and such terminology is favored in this discussion. The term "hormone" will be used for these factors since in general they seem to be hormone-like in their activity. How- ever, as will be seen below, the exact cor- respondence to a hormone as understood in vertebrate physiology is open to some ques- tion. The following terms, their definitions and synonomy are important. Brain Hormone. An agent produced by the protocerebrum, presumably by the neuro- secretory cells contained therein. It ac
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